Add subfloor appearance data, pipes correctly render subfloor. (#4393)

Content.Client/SubFloor/SubFloorShowLayerVisualizer.cs

@@ -0,0 +1,40 @@
+using Content.Shared.SubFloor;
+using JetBrains.Annotations;
+using Robust.Client.GameObjects;
+
+namespace Content.Client.SubFloor
+{
+    [UsedImplicitly]
+    public class SubFloorShowLayerVisualizer : AppearanceVisualizer
+    {
+        public override void OnChangeData(AppearanceComponent component)
+        {
+            base.OnChangeData(component);
+
+            if (!component.Owner.TryGetComponent(out SpriteComponent? sprite))
+                return;
+
+            if (component.TryGetData(SubFloorVisuals.SubFloor, out bool subfloor))
+            {
+                sprite.Visible = true;
+
+                // Due to the way this visualizer works, you might want to specify it before any other
+                // visualizer that hides/shows layers depending on certain conditions, such as PipeConnectorVisualizer.
+                foreach (var layer in sprite.AllLayers)
+                {
+                    layer.Visible = subfloor;
+                }
+
+                if (sprite.LayerMapTryGet(Layers.FirstLayer, out var firstLayer))
+                {
+                    sprite.LayerSetVisible(firstLayer, true);
+                }
+            }
+        }
+
+        public enum Layers : byte
+        {
+            FirstLayer,
+        }
+    }
+}