Floss: Prevent phone state desync with AG when answering/hanging up by HF.

For whatever reason(like network unstable), the call event sometimes not be able
correctly propagated to Call Center App.
When that happens, headset call state will desync with App because we
change the call state in HFP callback.

Fix the problem by only sending UHID event to App in HFP callback, and wait
until App sync the call state in dispatch UHID output.

Because when doing MPS qualification, there is no real app engage.
so here we directly jump right in to the telephony ops implementation

Bug: 331875859
Test: Conduct the following manual tests
  pair Bluetooth Headset
  Google Meet: headset is able hang-up the call
Test: Conduct the following manual tests
  pair Bluetooth Headset
  login Ring Central and place an incoming-call
  answer the call by headset
  hangup the call by headset
Test: Conduct the following manual tests
  pair Bluetooth Headset
  login Ring Central and place an incoming-call
  answer the call on Ring Central
  hangup the call from headset
Test: atest bluetooth_test_gd
Tag: #floss
Flag: EXEMPT, no behavior change on Android; Floss-only changes
Change-Id: I8e75725dbb3c8108fd81f6da3a311289d4177719