Add mechanism to register single task organizer

- Create a single task organizer in SysUI which registers as an organizer
  for multiple windowing modes internally in TaskOrgController.

Bug: 161980327
Test: atest WindowOrganizerTests
Test: atest SplitScreenTests
Test: atest PinnedStackTests
Test: atest ShellTaskOrganizerTests
Change-Id: Ic9dfbd6bcd75d9317e5a3aeb695afdff7e869d35