Merge changes I18245c22,I4c7a6085,I1c17b7f0,I663e5ad7,I9199fd92 into main

* changes:
  Completely destroy Launcher's Taskbar.
  Add context for sandboxing Taskbar window contexts.
  Add tests for TaskbarUnitTestRule.
  Have recreateTaskbar perform recreate on UiThread.
  Move test rules to subpackage.