Converts A && A.B into A?.B (#54342)

Implements the ?. operator, replacing code like A && A.B with A?.B

BYOND Ref:
When reading A?.B, it's equivalent to A && A.B except that A is only evaluated once, even if it's a complex expression like a proc call.

code/game/objects/structures/plasticflaps.dm

@@ -65,7 +65,7 @@
 		if(!M.ventcrawler && M.mob_size != MOB_SIZE_TINY)
 			return FALSE
 	var/atom/movable/M = caller
-	if(M && M.pulling)
+	if(M?.pulling)
 		return CanAStarPass(ID, to_dir, M.pulling)
 	return TRUE //diseases, stings, etc can pass