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

addons/csharp_ldtk_importer/LdtkImporter.cs

@@ -1,6 +1,29 @@
 using Godot;
 using System;
 
-public partial class LdtkImporter : Node
+namespace CSharpLdtkImporter;
+
+
+[Tool]
+public partial class LdtkImporter : EditorPlugin
 {
+    private LdtkResourceImporter _importer;
+    
+    public override void _EnterTree()
+    {
+        GD.Print("LdtkImporter: Plugin has been enabled.");
+        
+        _importer = new LdtkResourceImporter();
+        AddImportPlugin(_importer);
+        
+        GD.Print("LdtkImporter: Import plugin registered.");
+    }
+
+    public override void _ExitTree()
+    {
+        RemoveImportPlugin(_importer);
+        _importer = null;
+        GD.Print("LdtkImporter: Import plugin unregistered.");
+        GD.Print("LdtkImporter: Plugin has been disabled.");
+    }
 }