Allow AppHandles to report screen positions to interested parties

* Added a new class which takes updates to AppHandle positions and
forwards them to interested listeners.
* SystemUI components can access and add a listener via WMComponent

Bug: 397506207
Flag: EXEMPT bug fix
Test: Tested via logs to see both ends of listener are working

Change-Id: Ie0cb5b4915fdd44437bd4e578b3b0af99bbb5485