TaskbarManager now sets TaskbarUIController for RecentsWindowManager

- FallbackTaskbarUIController can take in a generic
  RecentsViewContainer parameter, i.e. RecentsActivity or
  RecentsWindowManager.
- When changing Overview targets to RecentsWindowManager, which is not
  an Activity, we still update the TaskbarUIController

Test: Switch between default Home activities with the flag on and off,
ensure Taskbar works as expected in each case (3P vs 1P launcher).
Flag: com.android.launcher3.enable_fallback_overview_in_window
Fixes: 368030750
Fixes: 365775636

Change-Id: Ife775e8c226f8c73ec9e1f97b4a6f2972f6c905f