Updating fields in New Unread-message broadcast

- Including BT device that new message notification is for. This will be
  helpful for messaging apps that need to handle incoming messages for
  different possible devices. When a device disconnects, all messages
  persisted from that device can be wiped.
- Switching extra used for sender fields. Using *RECIPIENT* fields was
  confusing and hence switching to new *SENDER* fields defined in
  BluetoothMapClient.

Bug: 33280056
Change-Id: I6bf410315801eeb7e869e86b807c8261e4ffae3f
Test: Manually