Fix SUW unstash animation.

- Defer any UI updates to taskbar after the SUW unstash animation is created.
- Predicted app icons take longer to load, so it's possible that they are
  added after the animation is created.
- This avoids the case where icons are seemingly in the taskbar but
  do not get animated like the rest of the icons.

- We also need to call onAnimationStart for the reveal animation immediately,
  otherwise the clipToOutline params never get set.

Bug: 277712185
Test: flash device, very quickly go through SUW
Change-Id: I4c3089da0d20bf91672e2305655c4c37b1f367aa