Floss: Add UHID Mute support

Bug: 277693919
Test: Conduct the following manual tests.
  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
  "Hook Switch", "Off-Hook", "Ring" and "Mute" test cases are passed
  used https://online-voice-recorer.com during "Hook Switch" and
    "off-Hook" tests to check audio input
  Google Meet: headset is able to mute, un-mute and hang-up the call
Test: atest bluetooth_test_gd

Change-Id: I294bdfb9aa66169042502a057615572260cf86a8