Add timecode based av dump mode

This mode would dump every audio sample exactly and every video frame exactly, with no duplicates, droplicates, stretching, or squeezing. It would also dump a separate timecodes file that gave the timing of each video frame. This should be doable in our system without significant changes.

The timecodes would be in a separate file and not dumped to the stream because most of our AV sinks either have no way at all to deal with VFR (AVI), or you wouldn't want to trust with VFR (ffmpeg).

Accordingly, the result would have severe desync if you tried to play it back without first doing something with the timecodes, so this option would default to false and only be for advanced users.

This would coincide with removing the sync to video option, as it has no purpose other than to enable exact video frame recovery in pathological situations that Bizhawk doesn't support well.

Start by locating the existing audio/video dump implementation and the sync-to-video option. Determine how audio samples and video frames are currently selected, then define the timecode file format and output behavior. Done means exact, non-duplicated samples and frames can be dumped with per-frame timing, while the new mode is disabled by default and sync-to-video is removed.