Test for switch animation

Add unit tests to check that when we switch between bubbles or bubble
and overflow, that the previous view is hidden and new view is shown.

Bug: 276747288
Test: atest WMShellMultivalentTestsOnDevice:com.android.wm.shell.bubbles.bar.BubbleBarAnimationHelperTest
Test: atest WMShellRobolectricTests:com.android.wm.shell.bubbles.bar.BubbleBarAnimationHelperTest
Flag: com.android.wm.shell.enable_bubble_bar

Change-Id: Ib6960fe9281d8cac8f0a2306743800cf8ef353be