Make ore loot use walls as a mask (#16377)

Content.Shared/Procedural/Loot/BiomeMarkerLoot.cs

@@ -0,0 +1,13 @@
+using Content.Shared.Parallax.Biomes.Markers;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+
+namespace Content.Shared.Procedural.Loot;
+
+/// <summary>
+/// Adds a biome marker layer for dungeon loot.
+/// </summary>
+public sealed class BiomeMarkerLoot : IDungeonLoot
+{
+    [DataField("proto", required: true, customTypeSerializer:typeof(PrototypeIdSerializer<BiomeMarkerLayerPrototype>))]
+    public string Prototype = string.Empty;
+}