immobilized (#52578)

Adds an immobilized trait.
    Adds procs for several variable changes so we can respond to their events.
    Adds some signals for said variables changing.

Need to turn the variation in number of usable legs and arms (get_num_legs() and get_num_arms()) into events we can respond to, but they are pretty annoying to do so. Probably for a different PR.

code/game/objects/items/robot/robot_parts.dm

@@ -304,8 +304,7 @@
 			log_game("[key_name(user)] has put the MMI/posibrain of [key_name(M.brainmob)] into a cyborg shell at [AREACOORD(src)]")
 
 			if(!locomotion)
-				O.lockcharge = TRUE
-				O.update_mobility()
+				O.set_lockcharge(TRUE)
 				to_chat(O, "<span class='warning'>Error: Servo motors unresponsive.</span>")
 
 		else
@@ -342,8 +341,7 @@
 			forceMove(O)
 			O.robot_suit = src
 			if(!locomotion)
-				O.lockcharge = TRUE
-				O.update_mobility()
+				O.set_lockcharge(TRUE)
 
 	else if(istype(W, /obj/item/pen))
 		to_chat(user, "<span class='warning'>You need to use a multitool to name [src]!</span>")