Make HearingAid code more generic

-handle UI updating when sub device connection state changes
-add test case

Bug: 112735753
Test: make -j42 RunSettingsRoboTests
Change-Id: Ie2643657c47a0956aac3f8cac4bfdbdea0399ce8

src/com/android/settings/bluetooth/BluetoothDetailsMacAddressController.java

@@ -51,6 +51,8 @@ public class BluetoothDetailsMacAddressController extends BluetoothDetailsContro
 
     @Override
     protected void refresh() {
+        mFooterPreference.setTitle(mContext.getString(
+                R.string.bluetooth_device_mac_address, mCachedDevice.getAddress()));
     }
 
     @Override