Properly run window animations at vsync-sf (1/2)

- Add new Choreographer instance that runs on vsync-sf
- Use this new Choreographer for WindowAnimator, and remove all
the hacks around it

Test: Open apps and close apps, notice no stutter
Test: Screen zoom animations
Test: go/wm-smoke
Bug: 36631902
Change-Id: I988ae25645effc3ac20efa7cb9b68f23444da0d0