Fixed Bubble Bar Cutoff After Unlock

The Bubble Bar was being cut off due to the taskbar window height.
Modified the BubbleBarViewController to rely on the bubble count to
compute the maximum height, rather than the BubbleBarView visibility.

Test: Manually tested. Expanded the Bubble Bar in 3-button navigation.
Pressed the power button to lock the screen. Unlocked the screen.
Fixes: 391358222
Flag: com.android.wm.shell.enable_bubble_bar

Change-Id: I1923fc84df403abea022ba84f23fc66be7dbe7aa