Extract dependencies for HeadsetStateMachine

* Isolated JNI native interface in a separate class
  HeadsetNativeInterface so that is can be mocked when testing
  HeadsetStateMachine
* Moved HeadsetStateMachine.StackEvent out as HeadsetStackEvent
* Restructured create(), start(), stop() and cleanup() methods in
  HeadsetService to create looper from a handler thread instead of using
  looper from main thread
* Added Javadoc to create, start, stop, and cleanup methods in
  ProfileService

Bug: 69005831
Test: runtest -j40 bluetooth
Change-Id: I7f68f734281415290ca5ca7fab8b20a6ee4a59fc