PBAP: multiple device support

* For each new connection, start a PBAP State Machine, and immediately
start accepting next incoming connection
* Store the map from BluetoothDevice to PbapStateMachine
* Use a unique number among range(1000000, 2000000) for the notification
ID in each PBAP State Machine
* Remove BroadcastReceiver for ACL_DISCONNECTED intent because this
event is already handled with OBEX close event

Bug: 69417672
Test: carkits with PBAP
Change-Id: Ie0d61220b0dba30a30167d932ac65b67c736f88d