Apply "most-recent" delivery policy to DREAMING related broadcasts.

This allows us to skip any older DREAMING_STARTED or
DREAMING_STOPPED broadcasts still waiting to be delivered to a
process when a new DREAMING_STARTED or DREAMING_STOPPED broadcast
is sent.

Bug: 255532556
Test: atest ./tests/tests/dreams/src/android/service/dreams/cts/DreamServiceTest.java
Change-Id: Ibc403aff4d0355a752aac30de7d733f294d2d91f