Support getting the accurate beat visual bounds

[comus111]

Problem

The beat visual height isn't accurate currently as it uses the barBounds.visualBounds.h in BeatContainerGlyph.buildBoundingsLookup.

beatBoundings.visualBounds.h = barBounds.visualBounds.h;

Expected

The beat visual rects should be something similar to the below red rects.

Use Cases

When mouse hovers on any beat, our app will show a tooltip for that beat. As there may be many beats, we want to highlight the hovered beat so that users can know which beat the tooltip is for.

[Danielku15]

Valid usecase, but the tricky bit is: there is a range of effects and annotations which might still expand the bounding boxes.

The expectation on what is included in the bounds might be different from user-to-user. For how I'd keep the existing "horizontal" offsets of what's included in the bounding box.

There are some tricky aspects to such a change:

1. AlphaTab doesn't precisely collect the bounding box of all elements. There might be some imprecisions and missing sizes to correctly calculate them.
2. The stems, beams, ties and tuplets handled on bar/measure level and are not directly drawn by the beats. Hence when building the bounds lookup, we need to respect such staff specific contents.

Any contributions to adapt the bounding box are welcome.

PS: the very last 3 notes are not own beats. They are "helper notes" of the "bend effect" and therefore belong to the main note/beat specifying the bend.