function addPipelineExtras(gltf) {
  ForEach.shader(gltf, function (shader) {
    addExtras(shader);
  });
  ForEach.buffer(gltf, function (buffer) {
    addExtras(buffer);
  });
  ForEach.image(gltf, function (image) {
    addExtras(image);
  });

  addExtras(gltf);

  return gltf;
}
Adds extras._pipeline to each object that can have extras in the glTF asset.
This stage runs before updateVersion and handles both glTF 1.0 and glTF 2.0 assets.

@param {object} gltf A javascript object containing a glTF asset.
@returns {object} The glTF asset with the added pipeline extras.

@private