Add Settings support for Bluetooth Multi-A2DP and Multi-HFP

When there are multiple connected A2DP/HFP devices, if a connected
device's name is clicked on, that device will be chosen as
Active - i.e., it will be the device chosen for audio out / phone call.

Test: Manual: multiple connected A2DP devices, and selecting each as
      the Active Device.
Bug: 64767509

Change-Id: Iee76286110ed87703d6a968f50273c22cd7c7086