The launcher to always listen to app widget

Making changes to AppWidgetHost and AppWidgetHostView to make sure

  1. We could make further changes the implementation of the listener in
     launcher

  2. There is backward compatibility by making AppWidgetHostView a
     listener

Design doc: https://docs.google.com/document/d/1QpTYeOvbpGlcOLe26BtMmpaN2_rG-EC1vn4eNo89zZs/edit?usp=sharing

Test: N/A
Bug: 235358918
Change-Id: I8c3cd4eee86d93dfdeb14b0dd6d086a49e1b3b18