BroadcastOption for "this is an alarm broadcast"

Instead of a callback/observer mechanism between the alarm subsystem and
the broadcast delivery subsystem, there will be a direct
BroadcastOptions tag that the Alarm Manager uses to annotate broadcasts
that originate from an alarm firing.  Only the OS itself can use this
BroadcastOptions annotation.

Bug: 161537193
Test: atest CtsAlarmManagerTestCases
Test: atest BroadcastOptionsTest
Test: atest FrameworksMockingServicesTests:AlarmManagerServiceTest
Change-Id: Ie45fd67f9dd55931a3dc109dc198c118b2a55bce