Fix some jank with transitions

- Animations in WorkspacePageIndicator while the app transition
was running was causing layer trashing, potentially leading to
jank.
- Make sure to use a layer in the wallpaper open animation.

Test: Open app while indicators are about to fade out.
Bug: 75985430
Change-Id: Iad6a511d98dff81b5cde727f4472f0f039ffc4be