[DNM][DNM][WIP] Projectile backend code port and update

Ports#54924,  #65061, #59804 from /tg.
adds auxiliary code from /tg to make code work.

code/game/objects/structures/grille.dm

@@ -5,6 +5,7 @@
 	icon_state = "grille"
 	density = TRUE
 	anchored = TRUE
+	pass_flags_self = PASSGRILLE
 	flags_1 = CONDUCT_1
 	pressure_resistance = 5*ONE_ATMOSPHERE
 	layer = BELOW_OBJ_LAYER
@@ -124,14 +125,10 @@
 	if(!shock(user, 70))
 		take_damage(20, BRUTE, "melee", 1)
 
-/obj/structure/grille/CanPass(atom/movable/mover, turf/target)
-	if(istype(mover) && (mover.pass_flags & PASSGRILLE))
-		return TRUE
-	else
-		if(istype(mover, /obj/item/projectile) && density)
-			return prob(30)
-		else
-			return !density
+/obj/structure/grille/CanAllowThrough(atom/movable/mover, turf/target)
+	. = ..()
+	if(!. && istype(mover, /obj/projectile))
+		return prob(30)
 
 /obj/structure/grille/CanAStarPass(ID, dir, caller)
 	. = !density