Add ability to track cursor outside of the window/scope

[esimkowitz]

Record the cursor position when it is outside the window/scope bounds so sliders don't abruptly stop moving if they go out of focus while still being tracked.

[esimkowitz]

Seems that setPointerCapture can solve this on Web. Need to figure out the best way to handle this on Desktop

[esimkowitz]

Here's the web-sys equivalent https://rustwasm.github.io/wasm-bindgen/api/web_sys/struct.Element.html#method.set_pointer_capture