Implement correct visitId/frameId logic for the FPS/MCS system.

ics_mcsActor is currently commanded directly by Gen2, so self-allocates frameIds. It has no context about its exposures (how many are being taken, etc.) so wastefully allocates full 100-frame visits for each frame.

When we switch to ics_fpsActor control, that will be able to fetch/receive a visit and tell the mcsActor about the individual frames within that.

Implement this. The only trick is that in operation, the fpsActor itself will be told what the active visit is. But that is pretty minor.