Convert a bunch of legacy overlay calls to SSoverlays (#4015)

Bunch of overlay conversions I found in an old stash I had forgotten about.

code/modules/reagents/Chemistry-Reagents/Chemistry-Reagents-Toxins.dm

@@ -559,7 +559,7 @@
 	M.transforming = 1
 	M.canmove = 0
 	M.icon = null
-	M.overlays.Cut()
+	M.cut_overlays()
 	M.invisibility = 101
 	for(var/obj/item/W in M)
 		if(istype(W, /obj/item/weapon/implant)) //TODO: Carn. give implants a dropped() or something

code/modules/reagents/reagent_containers/food/snacks.dm

@@ -307,7 +307,7 @@
 	J.alpha = 200
 	J.blend_mode = BLEND_OVERLAY
 	J.tag = "coating"
-	overlays += J
+	add_overlay(J)
 
 	if (user)
 		user.visible_message(span("notice", "[user] dips \the [src] into \the [coating.name]"), span("notice", "You dip \the [src] into \the [coating.name]"))
@@ -338,7 +338,7 @@
 		var/image/J = image(I)
 		J.alpha = 200
 		J.tag = "coating"
-		overlays += J
+		add_overlay(J)
 
 
 		if (do_coating_prefix == 1)

code/modules/reagents/reagent_dispenser.dm

@@ -131,12 +131,12 @@
 
 			rig = W
 			user.drop_item()
-			W.loc = src
+			W.forceMove(src)
 
-			var/icon/test = getFlatIcon(W)
-			test.Shift(NORTH,1)
-			test.Shift(EAST,6)
-			overlays += test
+			var/mutable_appearance/MA = new(W)
+			MA.pixel_x += 1
+			MA.pixel_y += 6
+			add_overlay(MA)
 
 	return ..()