PBAP: Use ACTION_CONNECTION_STATE_CHANGED intent

* Use ACTION_CONNECTION_STATE_CHANGED to broadcast connection state
  change to comply with BluetoothProfile interface requirement
* Use BluetoothProfile.STATE_* variables to represent connection
  states for PBAP profile

Bug: 63873163
Test: Connect to car kits
Change-Id: I7dfcfc1b3a3e4868ea5e313f62ad5e504d58b9c2