Android: Detect internal mic/audio out and enable Mute Myself by default

Another idea before I forget to write it down...

It would be nice to have if the Android audio system could check whether it's only got the internal mic / audio out connected. If so, it should turn on "Mute Myself" and prevent it being turned off. (Maybe have a different banner - so we'd have "unmuted", "self-muted" and "hard muted".)

_Originally posted by @pljones in https://github.com/jamulussoftware/jamulus/issues/2457#issuecomment-1058956170_

The issue does not name an Android audio file, entry point, or test. Start by locating the Android audio-system code that detects connected microphone and audio-output devices, then verify how mute state and its banner are represented. Done means internal-only audio enables “Mute Myself” by default, prevents unmuting, and distinguishes unmuted, self-muted, and hard-muted states.

Written by the indexing model from the issue text.