Add APIs to get remote device's battery level (1/2)

* Add BluetoothDevice.getBatteryLevel() API to retreive battery level
  information of remote device
* Add BluetoothDevice.ACTION_BATTERY_LEVEL_CHANGED intent to notify user
  that remote device's battery level has changed

Bug: 35874078
Test: make, pair with devices and use them
Change-Id: I41051ee25383f5f3a1e505aef6f8c526385f58bd
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 914099f..d5ac4ae 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -142,6 +142,7 @@
     <protected-broadcast android:name="android.bluetooth.device.action.CONNECTION_ACCESS_CANCEL" />
     <protected-broadcast android:name="android.bluetooth.device.action.CONNECTION_ACCESS_REQUEST" />
     <protected-broadcast android:name="android.bluetooth.device.action.SDP_RECORD" />
+    <protected-broadcast android:name="android.bluetooth.device.action.BATTERY_LEVEL_CHANGED" />
     <protected-broadcast android:name="android.bluetooth.devicepicker.action.LAUNCH" />
     <protected-broadcast android:name="android.bluetooth.devicepicker.action.DEVICE_SELECTED" />
     <protected-broadcast