mediarecorder: custom shortcut to stop- and start recording

[OneShot-Niko]

Why this would be helpful

Having to leave fullscreen just to stop or start a recording can get a bit annoying at times.

My suggestion

Allow the user to set a custom shortcut to stopping and/or starting a recording.

Possible alternatives

1. don't implement
2. Add a shortcut for it and don't implement

Additional context

No response

[DNin01]

If we add keyboard shortcuts, we may also want to add a recording indicator to the stage, so the user knows when a recording is in progress while they are not in the editor.

[DNin01]

Related: #4889