Add door welding (#1951)

* Add door welding

Surprised this wasn't in already.

* smug's feedback

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Resources/Prototypes/Entities/Constructible/Doors/airlock_base.yml

@@ -16,6 +16,8 @@
     - state: closed_unlit
       shader: unshaded
       map: ["enum.DoorVisualLayers.BaseUnlit"]
+    - state: welded
+      map: ["enum.DoorVisualLayers.BaseWelded"]
     - state: bolted
       shader: unshaded
       map: ["enum.DoorVisualLayers.BaseBolted"]