[MODDING] Add a callback that triggers when a NPC/Monster Moved

[Khanx]

Add a callback that triggers when a NPC/Monster moves, it can be helpful to detect when a monster moves over a trap.

[pipliz]

I've thought about it when adding traps to the game itself, but given the trap/monster counts involved the traps now work by checking for monsters often instead of the other way around. It's decently quicker to check whether a monster/NPC is at/near XYZ than to query the world for a block being near