Implement bubble bar flyout background animation

Update the bubble bar flyout drawing behavior to allow to animate
from a collapsed position into an expanded position.

This change only handles the rounded rect and the triangle. The
text is still left unchanged.

When wired up this looks like this:
left: http://recall/-/bJtug1HhvXkkeA4MQvIaiP/gIsckRmFKj8CceafiJnPTa
right: http://recall/-/bJtug1HhvXkkeA4MQvIaiP/dpn51yXFCCkT6ViUegf351

Flag: com.android.wm.shell.enable_bubble_bar
Bug: 277815200
Test: atest BubbleBarFlyoutViewScreenshotTest
Test: atest BubbleBarFlyoutControllerTest
Change-Id: I85ae3bf908c04e5473655c9e536495f56d80f466