Floss: Call IBluetoothTelephonyCallback method on UHid Open/Close events

The new added telephony callback expose the "in use" state, the main user
is the audio server to decide which of HFP and A2DP to use for audio.

Bug: 277693919
Test: Conduct the following manual tests.
  start btclient
  pair Bluetooth Headset
  load https://google.git.io/libhidtelephoony/ with Chrome
  click on "Start", select the headset then "Connect"
  "Inputs Reports" and "Output Reports" are correct
  btclient displays "Telephony use changed: …" events
Test: atest bluetooth_test_gd

Change-Id: Iabd179b72d1dba4ba75c95761a90ffb65e1bd41f