It's possible that ResizeManager will trigger its debounce handler but
then get disposed before the handler runs. This can cause tests to fail,
so, instead, we should cancel the debounce when ResizeManager is
disposed.
Because we add Touch Activity in the parent class and those don't actually get removed in Resize Manager we leak on every dispose. Calling super.dispose() cleans them up because we remove our list of handlers via a call to DomData.removeData
Fixes#5339
Use ResizeObserver when available for better and more performant resizing information, otherwise, fall back to a throttled resize event on an iframe that's the size of the player.
Allows a video.js user to disable this by setting resizeManager: false as an option since the component will not be initialized.
Add a debounce util.
This reverts #4800 (e0ed0b5) because we end up getting two playerresize events with the dimension methods now.
