Implement audio recording

[Megamouse]

Recording in general

• Adds an audio track to video recording (currently AC3 as proof of concept)
• The channel count matches the game's output channel count
• The recording expects 256 samples per block at 48000 samples per second
• We drop packages that are too early (should not really happen with regular recording)
• We add silence if we get packages too late in order to make the encoder happy and don't get desync.

cellRec

• Implements most features of cellRec audio encoding
• This includes internal cellAudio sources as well as external cellRec sources (external is untested)
• Always downmix to stereo, since cellRec only does 2 channels.
• Adds the external cellRec audio to the internal cellAudio with a volume factor
• Works with both the ringbuffer recording as well as the regular recording

Known issues

• Recorded audio may have crackling if the recording is paused and resumed.

implements #11874