Handle uid state changes on the handler thread.

onUidStateChanged callbacks are invoked on android.ui thread, so
to avoid blocking it for too long, offload the work to handle
the uid state changes to a different thread.

Bug: 289157124
Test: atest services/tests/mockingservicestests/src/com/android/server/am/BroadcastQueueTest.java
Test: atest services/tests/mockingservicestests/src/com/android/server/am/BroadcastQueueModernImplTest.java
Change-Id: I005ee6a7486ec1cc6dfe0c7ad4b488309dbda270