Reuse existing handle color when switching bubbles

Allow setting initial handle color if the region sampling has not been
enabled on the bubble bar expanded view handle.
When switching between bubbles, set the initial color for the handle as
the handle color of the currently open bubble.

Bug: 276747288
Test: atest BubbleBarHandleViewTest
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: If06b73985aa0adc07ce6ded3d809d961a58bbdfd