Add BatterySaverPolicy for power save mode

The BatterySaverPolicy is designed to consolidate all battery saver
knobs into a central location. Usually it is consistent to
mLowPowerModeEnabled unless it gets different data for specific
service. By adding these knobs, we can effectively tune the battery
saver.

This cl sets up the framework for BatterySaverPolicy and updates
following service to get battery saver data from BatterySaverPolicy

1. GnssLocationProvider
2. VibratorService
3. WindowManagerService
4. BackupManagerService
5. SoundTriggerService
6. NetworkPolicyManagerService

Screen brightness will come in a following cl.

Bug: 34693888
Test: FrameworksServicesTests

Change-Id: I6b040e93391614b44d136a485faa4a332c396e51