Recreate accidentally lost recording function

My ALSA state rework accidentally lost recording function, e.g. as
used by the Voice Notes application.  This commit recreates it.

I thought it might be possible for the default Media state - normally
MediaSpeaker - to handle both playback and recording.  But this
produces a nasty feedback loop, because Pulseaudio is by default
always looping the default source (i.e. the microphone) back to the
default sink (i.e. the speaker).  Therefore the default MediaSpeaker
can't have the microphone switch open, and therefore we need a
separate state, MediaRecording, to handle recording.

How then, does an application such as Voice Notes get the
MediaRecording state installed?  My guess is that it happens
automatically when any applications uses a QAudioInput, so long as all
the states have their Input/Output capabilities correctly defined.