Add sub-biomes (#17855)

Content.Shared/Parallax/Biomes/Layers/BiomeMetaLayer.cs

@@ -0,0 +1,27 @@
+using Robust.Shared.Noise;
+using Robust.Shared.Serialization;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+
+namespace Content.Shared.Parallax.Biomes.Layers;
+
+/// <summary>
+/// Contains more biome layers recursively via a biome template.
+/// Can be used for sub-biomes.
+/// </summary>
+[Serializable, NetSerializable]
+public sealed class BiomeMetaLayer : IBiomeLayer
+{
+    [DataField("noise")]
+    public FastNoiseLite Noise { get; } = new(0);
+
+    /// <inheritdoc/>
+    [DataField("threshold")]
+    public float Threshold { get; } = -1f;
+
+    /// <inheritdoc/>
+    [DataField("invert")]
+    public bool Invert { get; }
+
+    [DataField("template", required: true, customTypeSerializer: typeof(PrototypeIdSerializer<BiomeTemplatePrototype>))]
+    public string Template = string.Empty;
+}