Mouse drop refactor (#20256)

Refactored mousedrag procs, added signals, some safeguards, did some
cleanups around, renamed them to make a little more sense. Mostly put in
line with TG's code.
Fast clicking and releasing with a drag, depending on the grace period
and how fast it is done, can be counted as clicks, to aid in combat
scenarios where you spamclick.

code/game/objects/structures.dm

@@ -102,11 +102,11 @@
 		return TRUE
 	return FALSE
 
-/obj/structure/MouseDrop_T(mob/target, mob/user)
+/obj/structure/mouse_drop_receive(atom/dropped, mob/user, params)
 
 	var/mob/living/H = user
-	if(istype(H) && can_climb(H) && target == user)
-		do_climb(target)
+	if(istype(H) && can_climb(H) && dropped == user)
+		do_climb(dropped)
 	else
 		return ..()