Refactor Broadcasts related logic out of AMS.

This is a no-op refactor that moves the broadcasts
related code out of the AMS class. However, there is
still a portion of broadcasts related logic remaining
in AMS, which will be addressed in subsequent changes.

Bug: 361161826
Test: atest ./services/tests/mockingservicestests/src/com/android/server/am/ActivityManagerServiceTest.java
Test: atest ./services/tests/mockingservicestests/src/com/android/server/am/BroadcastQueueTest.java
Test: atest ./services/tests/mockingservicestests/src/com/android/server/am/BroadcastQueueModernImplTest.java
Flag: EXEMPT refactor
BYPASS_INCLUSIVE_LANGUAGE_REASON=Existing code

Change-Id: I1ecbbe50200cc9cf89da40bb6d9f4a4263234c07