Use region sampling to properly tint the bubble expanded view handle

* Create a RegionSamplingHelper when the taskview is shown
* Sampling only occurs while the view is visible and not being
  dragged
* RegionSamplingHelper is destroyed when the task is removed or the
  view is detached
* Added tests for BubbleBarExpandedView verifying when the helper
  is started / stopped appropriately
* Don't animate the handle color if it's the same

Minor unrelated change:
* Apply the caption insets when the TaskView is created, not on
  every layout pass

Test: atest BubbleBarExpandedViewTest
Test: manual - open a bubble, check that the handle is the right
               color, do something in the bubble that would change
               the handle color (e.g. put maps in a bubble and open
               an image of a location, check that handle color changes
               appropriately)
             - repeat above after dragging the bubble to the other
               side
             - repeat above after expanding / collapsing the bubble
Flag: com.android.wm.shell.enable_bubble_bar
Bug: 353160491
Change-Id: Ib3db46c416ec040cdad656df9be1841aed4b18e3