Allow power-allowlisted apps to schedule alarm-clocks

They can already use a lot of APIs to perform work in the background
and it simplifies the logic handling permission state changes and the
return value of canScheduleExactAlarms.

The major changes in behavior are:
1. Allowlisted apps can schedule unlimited alarm-clock alarms. This
should be the same as pre-S behavior.
2. If they happen to get the permission revoked, due to whatever reason:
user revocation, deny list, or app update, their alarm-clock alarms will
stay safe like their other exact alarms.
3. The API canScheduleExactAlarms is now true to its name: It returns
true even if the app is allowlisted.

Test: atest CtsAlarmManagerTestCases:ExactAlarmsTest
atest FrameworksMockingServicesTests:AlarmManagerServiceTest

BYPASS_INCLUSIVE_LANGUAGE_REASON=Existing APIs

Bug: 191716678
Bug: 190625528
Change-Id: I420694455f50aac10cf49cd43ff3b98575d86e9f