Injector sprite fix (#9011)

Content.Shared/SubFloor/SharedSubFloorHideSystem.cs

@@ -184,4 +184,9 @@ namespace Content.Shared.SubFloor
         Covered, // is there a floor tile over this entity
         ScannerRevealed, // is this entity revealed by a scanner or some other entity?
     }
+
+    public enum SubfloorLayers : byte
+    {
+        FirstLayer
+    }
 }

Content.Shared/SubFloor/SubFloorHideComponent.cs

@@ -1,4 +1,6 @@
 using Robust.Shared.GameStates;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Generic;
 
 namespace Content.Shared.SubFloor
 {
@@ -43,6 +45,13 @@ namespace Content.Shared.SubFloor
         [DataField("scannerTransparency")]
         public float ScannerTransparency = 0.8f;
 
+        /// <summary>
+        ///     Sprite layer keys for the layers that are always visible, even if the entity is below a floor tile. E.g.,
+        ///     the vent part of a vent is always visible, even though the piping is hidden.
+        /// </summary>
+        [DataField("visibleLayers", customTypeSerializer:typeof(CustomHashSetSerializer<object, AppearanceKeySerializer>))]
+        public HashSet<object> VisibleLayers = new() { SubfloorLayers.FirstLayer };
+
         /// <summary>
         ///     The entities this subfloor is revealed by.
         /// </summary>