title: Export gltf model with Instancedmesh
body: <p>I tried to export a cube of spheres create with the following code using instancedmesh as gltf model but upon importing it in blender it only shows one sphere (the original sphere).
  is there any way to export the instances as well and import the whole scene in blender as it is in threejs?</p>
  <pre><code>let scene, camera, renderer;
  let wrapper, canvas;
  function createWorld() {
      renderer.setClearColor(0x808080);
      scene = new THREE.Scene();
      camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 1, 10000);
      camera.position.z = 30;
      let light = new THREE.DirectionalLight(0xffffff, 0.8);
      light.position.set(0, 0, 1);
      camera.add(light);
      scene.add(camera);
      scene.add(new THREE.AmbientLight(0x303030));
      const material = new THREE.MeshLambertMaterial();
      const geometry = new THREE.SphereGeometry(0.45, 32, 16);
      const count = 11 * 11 * 11;
      let object = new THREE.InstancedMesh(geometry, material, count);
      let matrix = new THREE.Matrix4();
      let color = new THREE.Color();
      let i = 0;
      for (let z = -5; z &lt;= 5; z++)
          for (let y = -5; y &lt;= 5; y++)
              for (let x = -5; x &lt;= 5; x++) {
                  color.r = (x + 5) / 10;
                  color.g = (y + 5) / 10;
                  color.b = 1 - (z + 5) / 10;
                  object.setColorAt(i, color);
                  matrix.makeTranslation(x, y, z);
                  object.setMatrixAt(i++, matrix);
              }
      scene.add(object);
  }
  
  function render() {
      renderer.render(scene, camera);
  }
  
  function init() {
      try {
          renderer = new THREE.WebGLRenderer({
              canvas,
              antialias: true,
          });
          renderer.setSize(window.innerWidth, window.innerHeight);
          renderer.setPixelRatio(window.devicePixelRatio);
          renderer.toneMapping = THREE.ACESFilmicToneMapping;
          renderer.toneMappingExposure = 1;
          renderer.outputEncoding = THREE.sRGBEncoding;
      } catch (e) {
          wrapper.innerHTML = '&lt;h3&gt;&lt;b&gt;Sorry, WebGL2 is required but is not available.&lt;/b&gt;&lt;h3&gt;';
          return;
      }
  
      createWorld();
  
      let controls = new OrbitControls(camera, renderer.domElement);
      controls.enablePan = false;
      controls.enableZoom = false;
      controls.addEventListener('change', render);
  
      render();
  }
  
  init();
  </code></pre>