Floss: Add CallSource to CallInfo

In order to maintain call list status correctly, this design choose to
separate the call source from CRAS and HID device.
It won’t affect the call list status of CRAS, and it only maintains call
source from HID device in this feature.

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" and "Ring" test cases are passed
  used https://online-voice-recorer.com during "Hook Switch" test to check
    audio input
  Google Meet: headset is able to hang-up the call
Test: atest bluetooth_test_gd

Change-Id: I7270de77884630b74a41a990b658988204565c9e