Move AlarmManager to apex

Mechanical refactoring to move all except native code to the apex
directory. Accesses across the jar boundary will be cleaned up in
follow-ups.
Also, moved alarm manager code into its own package for better
organization.

Test: Buids, boots. Existing tests:
atest FrameworksMockingServicesTests:AlarmManagerServiceTest
atest CtsAlarmManagerTestCases

Bug: 151976605
Change-Id: Ida46491c1f1dff02dce4c50d3fafd4efbf977766