Rename MonitoredDeviceState to DeviceMonitor

Also:
- Don't make InputDevicesChangedListener part of the BatteryController
  interface, since it's not used for testing.
- Report a copy of the battery state when notifying components outside
  of BatteryController, becuase reporting a member object would
  leak the internal state to other components.
- Explicitly mark all interface methods as public.

Bug: 243005009
Test: atest FrameworkServicesTests
Test: atest FrameworkCoreTests

Change-Id: Iefa08f4f1b52b8dd48dc273e90e90c92d15d4ed4