2/ Add path for feeding rotation watcher signals to RotationButtonController

- A new rotation button controller is created for each nav/task bar as
  the controller currently is coupled with the view that it updates.
  Since the controller needs to listen for rotation watcher signals,
  we need to pull that out into a persistent place in NavBarHelper for
  the nav bar, but the taskbar flow will continue to use the controller
  to register for these changes.
- Because the flow is now from NavBarHelper -> NavBar -> RBC, we can
  also remove the existing callback from RBC -> NavBar

Bug: 219035565
Test: atest NavBarHelperTests
Test: atest SystemUITests
Change-Id: I2e26d0ce8f4184d1deb25300875ebf9035d7c538