Fix bugs found for app handle reporting

1. Position should take split apps into account (offset app handle
   bounds if in split)
2. Caption should not be updated onGlobalLayout since this means it will
   not happen if the handle is already laid out
3. Caption state should be reported using a MutableSharedFlow rather
   than a mutable state flow. This is because the app handle state of
   two apps may be emitted around the same time and a state flow will
   only take into account the latest one. We need all states to be
   handled.

Bug: 412444236
Test: manual testing
Flag: com.android.window.flags.enable_app_handle_position_reporting
Change-Id: Iaf6a539a14d57241c5b8b8af23bc5224720aa0d6