HFP: Split system interactions into HeadsetSystemInterface

* Split the interactions with other system services including but not
  limited to Audio, Power, Telecom, to a single class,
  HeadsetSystemInterface
* This allows us to synchronize system service calls in one place as
  they might come from separate state machines
* This also allows us to use a single SystemInterface instance for all
  running state machines so that each state machine does not need to
  create its own copy of the system interface objects
* Removing SET_MIC_VOLUME and INTENT_BATTERY_CHANGED messages from
  HeadsetStateMachine as they can be handled externally
* Adding INTENT_CONNECTION_ACCESS_REPLY message as this needs to be
  handled within the state machine asynchronously
* Use private classes instead of anonymous classes in HeadsetPhoneState

Bug: 68952570
Bug: 70678594
Test: runtest -j40 bluetooth, testplans/details/133403/3975
Change-Id: I98642a2296cf90c74c002fb254c6ace4785d898b