Add API to specify background color for animations

To be used for new task transtion animations
(go/android-new-task-motion) to set a background color behind the
animations instead of showing the wallpaper.

Test: atest FlickerTests:TaskTransitionTest
Bug: 199507257
Change-Id: I7fabfdcaf90be63c11eb3b18d65259c620570cab
5 files changed