Bluetooth: Display battery level of connected devices

* Add handler for BluetoothDevice.ACTION_BATTERY_LEVEL_CHANGED intent
* Check battery level information when UI is updated
* Show battery level in Quick Settings connected device summary line
* Show battery level in Bluetooth Settings connected device summary line
* Show battery level in Bluetooth device details page device summary
  line
* Add unit test for CachedBluetoothDevice, change HeadsetProfile and
  HidProfile to not final to enable mocking

Bug: 35874078
Test: make, unit test, connect to remote devices, connect/disconnect
      profiles
Change-Id: I729048cace73aab29337a8002a2897d2acf22fa6