Move sparkle animation to RenderThread

The sparkle loop animation was happening on the UI thread and is poses
some interesting challengers:
- Animations freezes when UI thread is busy, for example when
  startActivity is called.
- onDraw calls add unnecessary work to the UI thread, leading to jank
  in some cases, like PIP

Test: manual
Fixes: 184760248
Change-Id: Ie2840c767da61476678839eaac215dc3aff95b5c