Use "frozen" state for broadcasts.

We originally had been using registerUidObserver() to observe changes
to the "cached" state changes of apps, since that's all we had at
the time.  Since then, registerUidFrozenStateChangedCallback() has
been added, so this change pivots to using that.

Even though we internally have the ability to control per-process
broadcast queues, both of these listeners only provide UID-level
granularity, so we follow their lead.  If the freezer team adds PID-
level events in the future, we can easily adapt.

Bug: 276243219, 275142200, 275594411
Test: atest FrameworksMockingServicesTests:BroadcastQueueTest
Test: atest FrameworksMockingServicesTests:BroadcastQueueModernImplTest
Test: atest FrameworksMockingServicesTests:BroadcastRecordTest
Change-Id: Ia33cca1034fba9225f1fdbe97c216f077c4d9dba