Import of jpka changes for rack UI rework

[falkTX]

Imported as clean PR for easier review, text from changelog follows:

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Changes are (mostly) Rack view UI/UX.

FRONT SIDE

New knobs for 4 skin groups (internal, calf, openav, zynfx).
Added pushbuttons for booleans, and integers @ (selectable) [0,1] or [0,1,2] ranges. The idea is to make buttons well different from knobs, while still keep skin style, include disabled items.
Added several types of output parameter displays. There is no more non-shown controls now. Note: displays for non-default skins are WIP (but works). Feedback welcome.
All of these are fully scalable now (hidpi welcome).
All widgets have hover enlighting.
All widgets use HSL color model, so more color options presented, include high contrast tweak (see Tweaks).
Mouse wheel fixed (#11) and gives exact control for bools/ints, while smooth one for floats. Use with Ctrl and/or Shift to get four increment speeds/steps (fast, normal, fine, extra fine). Mouse drag also now have these four. Left mouse button toggles pushbuttons. Middle button set default value, double click edits it (#1569, #1570).
Hotkeys introduced when mouse hover active (no mouse press need) for both pushbuttons and knobs: 0...9 to set absolute value; Home, End, PgUp, PgDn. Note: 'Home' interferes with Canvas control hotkey (use 0 then, it's same).
Knob context menu unified and updated, have now hotkey suggestions.
Rack context menu enhanced, include group change of skin was added.
Tooltips with eyecandy precisions added.
Scalepoint tooltips added.
Custom colors are now match q'ty of displayed controls; gradients are can be easily set by any hue from/to (see Tweaks).
Solved some more UI tickets.
Many other "small" UI/UX fixes/improvements, like #1934.
Added pusheable Wet & Vol buttons, act now as Bypass (Thru line) and Mute (#52). Idea to make wet/vol knobs working as pusheable encoders. Previous state restored on un-push. Tested with remote control. Auto un-bypass on normal mouse drag (with lost of prev. value). Single click & 0 and Space keys on hover activated. Also see Tweaks.
Scalepoints for knobs and pushbuttons now cycled with Space key on hover, or left click; while still allowing to select intermediate states (if any) with keyboard shortcuts or mouse wheel (as with "normal" knobs/buttons). Note that Space key does nothing on "normal" knob (yet), and cycles "normal" pushbutton.
Fixed #1478.
Added Stereo panning, and also Front-Rear balance for 3-ch (like Stereo+Bass) and 4-ch plugins (for > 4-ch, only first four are tuned), along with classic L, R knobs. They all are not mutex now and can be combined. Not used control not eat extra DSP. It is saveable and remotely controlled as usual. Note: Classic L, R are special type mixing knobs; while newly added panning can only reduce amplitudes, but never increase.
Knob light arc starts from center for symmetrical span values (-N to N) (tweakable). (For default skin yet).
New scalable Tube skin added. Bakelite, glass, magic eyes, VFDs, neon indicators and argon filled "tuneon" bargraphs. Nixies created using true arcs. Nixies are used for display integers @ [0..(1..19)] span. Added pointer-style (chickenhead) knob for integer selectors (for tube skin yet). Ideas how it should look for other skins, are welcome.
XY controller knobs are updated to make it all scalable.
XY controller mouse buttons behaviour enhanced. Left button works as before. Right button gives smooth movement, like using 'smooth' checkbox. Middle button resets to center, include per-axis action when used on knob. And right and middle buttons can be joined, so allows to reset smoothly. Ctrl, Shift makes smoothing slower and faster. Reversed Y scale parameter added (see below).
Fixed #1979 (main problem, but not error messages).
XY controller enhanced to un-tie directly connected out X, Y ports from input ones, this not only makes external input possible, but also allow to use smoother between them, not on screen pad only. Let's try to connect discrete On-Off pedal to input and get flow of smoothed MIDI values on output: this ramp (slope) control is well suitable for synth's LFO, filter, or other smooth control. Note: GUI should be opened, even when external input control used only.
Three input control parameters were added to XY controller: speed, reversed Y axis, and linear smoothing. All controls are now exposed as input ports.
Added optional program (preset) drop-down list (similar to '(m)presets') on most skins, include compacted ones.
Added 'Reload' file. This "dangerous" option disabled out-of-box, only visible/working when its tweak enabled by user. It quick-reloads currently opened file, and any changes will be lost. It is intended for plugin developers mostly. Note: plugin libraries can be cached by system, so may not be refreshed with this "warm" restart.
New icons added. Icon labels now can be hidden via menu, if this new stuff does not fit on toolbar.
#312 semi-fixed, using 'Mute all' now available on toolbar, then enable one plugin by its volume knob push.
New Xray tab added to Edit dialog.
Fixed my own bug with miss of newly-added Qt6 items at qt_compat glossary.
Tweaks added, include per-skin. This is string of 'TweakName1':Value, 'TweakName2':Value, 'skinnameTweakName':Value, ... at Settings -> Configure Carla dialog. They are tunes many Rack display settings, and saved at same place as other settings (per-user, not per .carxp files). Default settings are selected to be most close to classic look, except that some controls, which were thrown away before, are shown now out-of-box: most notably, buttons. Note: Tweaks are WIP, suggestions welcome!

Tweak examples:

'ShowPan':0, Show Panning knob on rack (if plugin can Balance)

'ShowForth':0, Show Forth knob (Front-Rear balance) on rack (if plugin can Balance)

'WetVolPush':0, Wet&Vol knobs are pusheable with keyboard/mouse to Bypass and Mute #52

'WetVolPushLed':1, 0=Use classic look; 1=Use LED to display Bypass or Mute state

'WetVolOnCompact':0, Dry/wet, Volume knobs visible on Compacted slots #1884, #1923

'Tooltips':0, Show tooltips (note, it eats some CPU)

'MoreSpace':0, Compact some areas to give more free space to knobs

'GapAuto':0, Expand inter-knob gap to fit either label length or GapMin, but not more than GapMax #1919

'ShortenLabels':1, 0=Do not use smart name shortener, see GapAuto

'GapMin':0, value (px)

'GapMax':100, value (px)

'KnobTravel':(undefined), Or per skin like 'tubeKnobTravel':300, angle span (travel) of knobs.

'SymmetricArc':0, Knob light arc starts from center for symmetrical span values

'ColorFollow':0, Use plugin panel color tint to colorizing of widgets on this panel

'ButtonHaveLed':1, 0=LEDs are off of buttons (better for display 3-state buttons) (not all skins)
1=LEDs are on buttons (much adorable look)

'ColoredNeon':1, For Tube skin, 1 = show pushbuttons state (neon lamp) with color
0 = show pushbuttons state (neon lamp) with brightness

'HighContrast':0, Widgets becomes brighter by make it almost monochrome

'ShowDisabled':0, Show disabled input and output controls (debug mostly)

'ShowOutputs':1, Show output parameters, 0=Default

'ShowButtons':1, Show pushbutton instead of knob when applicable (see News)

'Button3Pos':1, 0=Buttons are integers with [0,1] range, 1=with [0,1,2] range

'TwoLineLabels':0, TODO

'ShowPrograms':0, These four tweaks shows
'ShowMidiPrograms':0, Program, or MIDI preset selector
'ShowProgramsOnCompact':0, (or both) when they are exist within
'ShowMidiProgramsOnCompact':0, plugin. It's safe to just enable all.

'ColorFrom':-0.1, value (float -1.0 to 1.0) "Rainbow" gradients used when ColorFollow=0

'ColorSpan':0.4, value (float -1.0 to 1.0) "Rainbow" gradients used when ColorFollow=0

'Auto7segSize':0, Override internal per-skin pre-tuned 7 segment displays look

'Auto7segWidth':1, Override internal per-skin pre-tuned 7 segment displays width

'ShowReload':0, Developers option: quick-reloads currently opened file. Changes will be LOST!

COMPILE

With Qt5: make clean && make
With Qt6: make clean && make FRONTEND_TYPE=6

Hotkeys on mouse hover

See #1971 ticket for key list.

REAR SIDE

Png/svg substrate stuff removed from rack skins bottom (knob) area.
QDial replaced to QWidget, else impossible to solve #11, and due to all methods of QDial we have already replaced anyway. Also somewhat refactored (lesser function calls) in hope to get a bit more performance.
Tested for CPU usage.
Zynfx internal stuff commented out, in prefer of external Zyn plugins, which are tested (have both int. and ext. is looks like mutually exclusive currently).
#1478 fix if for LADSPA and LV2 for now, others are i need more info how to test.
Extra python deps: TODO

Drawback: The code is runs more and more away from original one. While i try to make least possible intervention, but make it all works requires deep changes sometimes.

FILELIST

(diff -ur Carla/source/ Carla.my16/source/ | grep -v '^Only in' > source.patch)

patch -b -p1 < ../source.patch

patching file source/backend/CarlaBackend.h
patching file source/backend/CarlaHost.h
patching file source/backend/CarlaPlugin.hpp
patching file source/backend/CarlaStandalone.cpp
patching file source/backend/engine/CarlaEngine.cpp
patching file source/backend/engine/CarlaEngineNative.cpp
patching file source/backend/engine/CarlaEngineOsc.hpp
patching file source/backend/engine/CarlaEngineOscHandlers.cpp
patching file source/backend/engine/CarlaEngineOscSend.cpp
patching file source/backend/plugin/CarlaPlugin.cpp
patching file source/backend/plugin/CarlaPluginFluidSynth.cpp
patching file source/backend/plugin/CarlaPluginInternal.cpp
patching file source/backend/plugin/CarlaPluginInternal.hpp
patching file source/backend/plugin/CarlaPluginLADSPADSSI.cpp
patching file source/backend/plugin/CarlaPluginLV2.cpp
patching file source/backend/plugin/CarlaPluginNative.cpp
patching file source/frontend/carla_backend.py
patching file source/frontend/carla_backend_qtweb.py
patching file source/frontend/carla_host.py
patching file source/frontend/carla_host_control.py
patching file source/frontend/carla_settings.py
patching file source/frontend/carla_shared.py
patching file source/frontend/carla_skin.py
patching file source/frontend/carla_widgets.py
patching file source/frontend/qt_compat.py
patching file source/frontend/widgets/collapsablewidget.py
patching file source/frontend/widgets/commondial.py
patching file source/frontend/widgets/digitalpeakmeter.py
patching file source/frontend/widgets/paramspinbox.py
patching file source/frontend/widgets/pixmapkeyboard.py
patching file source/frontend/widgets/racklistwidget.py
patching file source/frontend/widgets/scalabledial.py
patching file source/frontend/xycontroller-ui
patching file source/native-plugins/xycontroller.cpp
patching file source/rest/carla-host.cpp
patching file source/rest/rest-server.cpp
patching file source/utils/CarlaBackendUtils.hpp
patching file source/utils/CarlaStateUtils.cpp
patching file source/utils/CarlaStateUtils.hpp

patch -b -p1 < ../resources.patch

patching file resources/resources.qrc
patching file resources/ui/carla_edit.ui
patching file resources/ui/carla_host.ui
patching file resources/ui/carla_settings.ui
patching file resources/ui/xycontroller.ui

add to resources/16x16/

add-from-favorites.svgz
add-jack-alt.svgz
add-jack.svgz
audio-volume-medium.svgz
audio-volume-muted-orig.svgz
audio-volume-muted.svgz
balance-alt.svgz
balance-alt2.svgz
balance.svgz
compact-alt.svgz
compact.svgz
dry.svgz
emblem-favorite.svgz
restore-alt.svgz
restore.svgz
skin.svgz
system-shutdown.svgz
system-turnon.svgz
view-refresh-purple.svgz
wet.svgz
--------- Total: 20