PiP: Refine pinch-resizing by damping rotation.

This adds:
- push back rotation starting by 5 degrees. Until the user input has
more than 5 degrees of rotation, we assume the user doesn't really want
to rotate it and only want to move/resize, so it's less jarring/jittery.
- Dampen the rotation once the user rotates past a certain amount.

Bug: 181068706
Test: Manual.
Change-Id: I0fd95d9cb2ad2eff053ce92817af22513d11cc62