Document Moved() and forwards old_locs (#59819)

- Passes the proper arguments on Moved(), forgot to do this on another PR.
- Documents the proc better.
- Cleans up code a little.

code/game/atoms_movable.dm

@@ -385,7 +385,7 @@
 
 	var/list/old_locs
 	if(is_multi_tile_object && isturf(loc))
-		old_locs = locs.Copy()
+		old_locs = locs // locs is a special list, this is effectively the same as .Copy() but with less steps
 		for(var/atom/exiting_loc as anything in old_locs)
 			if(!exiting_loc.Exit(src, direction))
 				return
@@ -440,7 +440,7 @@
 	if(oldarea != newarea)
 		newarea.Entered(src, direction)
 
-	Moved(oldloc, direction)
+	Moved(oldloc, direction, FALSE, old_locs)
 
 ////////////////////////////////////////
 
@@ -542,13 +542,21 @@
 	if(. && has_buckled_mobs() && !handle_buckled_mob_movement(loc, direct, glide_size_override)) //movement failed due to buckled mob(s)
 		return FALSE
 
-//Called after a successful Move(). By this point, we've already moved
-/atom/movable/proc/Moved(atom/OldLoc, Dir, Forced = FALSE)
+
+/**
+ * Called after a successful Move(). By this point, we've already moved.
+ * Arguments:
+ * * old_loc is the location prior to the move. Can be null to indicate nullspace.
+ * * movement_dir is the direction the movement took place. Can be NONE if it was some sort of teleport.
+ * * The forced flag indicates whether this was a forced move, which skips many checks of regular movement.
+ * * The old_locs is an optional argument, in case the moved movable was present in multiple locations before the movement.
+ **/
+/atom/movable/proc/Moved(atom/old_loc, movement_dir, forced = FALSE, list/old_locs)
 	SHOULD_CALL_PARENT(TRUE)
 
 	if (!inertia_moving)
 		inertia_next_move = world.time + inertia_move_delay
-		newtonian_move(Dir)
+		newtonian_move(movement_dir)
 	if (length(client_mobs_in_contents))
 		update_parallax_contents()
 
@@ -556,7 +564,7 @@
 	if(move_stacks > 0)
 		return
 
-	SEND_SIGNAL(src, COMSIG_MOVABLE_MOVED, OldLoc, Dir, Forced)
+	SEND_SIGNAL(src, COMSIG_MOVABLE_MOVED, old_loc, movement_dir, forced, old_locs)
 
 	return TRUE