Timer based pointer event resampling

This provides two improvements to pointer event resampling:

1. PostFrameCallbacks are used instead of scheduling frames. This
avoids unnecessary rendering work when resampling is used.

2. Resampling continues when frames are not produced. I.e. input
events keep being delivered at a fixed frequency even if frame
production is taking a long time.

This fixes #72924
Co-authored-by: David Reveman <reveman@google.com>
Co-authored-by: Tong Mu <dkwingsmt@users.noreply.github.com>