Multi HFP connection handling

The basic handling mechanism is to create multiple state machines for
each connection. We route the upper layer (application) and lower layer
(callbacks) appropriately depending on the BluetoothDevice.

The following are implemented:
-- StateMachine creation (garbage collection/deletion still needs work)
-- Device awareness in service to route the messages
-- Cleanup of code and creating a new class for handling native messages

You can do the following with this change:
-- Create multiple connections (simultaneously)
-- Tear down connections

Bug: b/33554547
Bug: b/30984220

Change-Id: If08f24f744b046a393e836c99fcf2288fd698cc2