Support expanding the bar while animating

Update the BubbleBarAnimator to handle auto expanding bubbles as
well as expand signals that are received while animating the bubble
bar.

The expansion starts after the bar reaches its peak height. If the
hide animation starts before the expansion signal is received, we
ignore it.

Next step is to delay showing the expanded view until the bubble bar
starts expanding.

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 353644484
Fixes: 356415377
Bug: 339683389
Test: atest BubbleBarViewAnimatorTest
Change-Id: I79a63f0b8728abc1ab3345f0116cbfcba2918643