Allow IVoiceInteractionSessionListener to listen for window vis changes

- The listener currently tracks session shown/hidden, but doesn't track
  the visibility of the session window which can change on the client
  side without the server knowing. In some cases, it's useful for SysUI
  to be able to track the visibility of the session window to show/hide
  bars appropriately.

Bug: 222308557
Test: Manual, launch the assistant and verify the calls are made
Change-Id: I9b4bb27c9497b2a828616caf72eaf345b072c294