[remoting host][mac] Add routine to list audio devices

It isn't straightforward for the user to figure out the UID of an audio
device, so this CL provides an extra host routine to list all available
audio devices and their UID. The user can trigger it by running:

  remoting_me2me_host.app/Contents/MacOS/remoting_me2me_host --list-audio-devices

An example output looks like this:

  Audio devices:
    Device name: BlackHole 16ch
    Device UID: BlackHole_UID

    Device name: MacBook Pro Microphone
    Device UID: BuiltInMicrophoneDevice

    Device name: MacBook Pro Speakers
    Device UID: BuiltInSpeakerDevice

Bug: 1161363
Change-Id: I060d08956a9635cb6d8e165a90f891399fb63be5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2630741
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844323}