add initial implementation of LDtk importer with data models and scene builder

addons/csharp_ldtk_importer/Models/LdtkLayerInstance.cs

@@ -0,0 +1,27 @@
+using System.Text.Json.Serialization;
+
+namespace CSharpLdtkImporter.Models;
+
+public class LdtkLayerInstance
+{
+    [JsonPropertyName("__identifier")]
+    public string Identifier { get; set; }
+
+    [JsonPropertyName("__type")]
+    public string Type { get; set; }
+
+    [JsonPropertyName("__gridSize")]
+    public int GridSize { get; set; }
+
+    [JsonPropertyName("__tilesetDefUid")]
+    public int? TilesetDefUid { get; set; } // Nullable for entity layers
+
+    [JsonPropertyName("gridTiles")]
+    public LdtkTileInstance[] GridTiles { get; set; }
+    
+    [JsonPropertyName("autoLayerTiles")]
+    public LdtkTileInstance[] AutoLayerTiles { get; set; }
+
+    [JsonPropertyName("entityInstances")]
+    public LdtkEntityInstance[] EntityInstances { get; set; }
+}