BatteryController: Add battery monitoring from Bluetooth

For input devices that are connected over Bluetooth, we will monitor
their Bluetooth battery state by registering a BroadcastReceiver to
listen to battery changes over Bluetooth.

We always prioritize reporting the Bluetooth battery state first, and if
invalid, fall back to using the battery state queried through the sysfs
node.

In this CL, we add a BluetoothBatteryManager interface to hide the
details of dealing with the Bluetooth APIs to simplify testing.

Bug: 243005009
Test: atest FrameworkServicesTest
Test: manual, with Lenovo Precision Pen 3
Change-Id: I40864c0aeaf72c252a5f8d0b2217903613ca9543