For Auto, display battery status as that of a connected device.

For Android Auto Embedded, we would like to display the battery status
of a device that is connected via Bluetooth and not the battery status
of the device itself (which would not make sense in Auto).

To accomplish this, introduce a new CarBatteryController that only
monitors the status of battery via Bluetooth. Note that AAE is not
explicitly handling the battery icon that appears in the quick settings
because this will be hidden for Auto.

This CarBatteryController implements a new BatteryController interface.
What used to be the BatteryController has been moved to the
BatteryControllerImpl class.

Bug: 28002775
Change-Id: I2285bcbd3d207cdcc1ac5a98ec3685d4fff0f0d9