Help Requested: INotifyActorMovement

I need help with the Lua tie-in and testing. I've haven't had much time to spend on this over the past three weeks, and rather than let it lie stagnant, I figured asking for help.

Closes  #6204. (Or meant to)

Pinging @obrakmann as he knows a bit about this.

(Sidenote: I've attempted to use this same code for shroud and crushing, but once you have 300+ listeners + movers the lag becomes visible, so I've restricted this to region checking for now.)
it would be nice to have
1) a flag on the region to specify whether it can be activated multiple times. A bool `Repeatable` or something like it in the Info class should work.
2) a way to rate-limit the number of notifications. As an idea, add a field that stores the frame number of the last notification, and then have field in the Info class that contains the delay until next activation in ticks.