message: Fix bug in glTF scenes containing HDRI light.  Loading changed.
  HDRI light definition changed so that lights loads texture at
  pre-commit time -- allowing HDRI in .sg files.  glTF needs to
  handle them slightly differently now.
diff: @@ -226,8 +226,7 @@ void GLTFData::applySceneBackground(NodePtr bgXfm)
  auto &bgFileName = background.Get("background-uri").Get<std::string>();
  rkcommon::FileName bgTexture = fileName.path() + bgFileName;
  auto bgNode = createNode("background", "hdri");
  - auto &map = bgNode->createChild("map", "texture_2d");
  - map.nodeAs<sg::Texture2D>()->load(bgTexture, false, false);
  + bgNode->createChild("filename") = std::string(bgTexture);
  if (background.Has("rotation")) {
  const auto &r = background.Get("rotation").Get<tinygltf::Value::Array>();
  @@ -327,13 +326,8 @@ void GLTFData::createLights()
  "penumbraAngle", "float", outerConeAngle - innerConeAngle);
  } else if (l.type == "hdri") {
  newLight = createNode(lightName, l.type);
  - auto &hdriTex = newLight->createChild("map", "texture_2d");
  - static rkcommon::FileName texFileName("");
  auto hdrFileName = l.extras.Get("map").Get<std::string>();
  - texFileName = fileName.path() + hdrFileName;
  -
  - auto ast2d = hdriTex.nodeAs<sg::Texture2D>();
  - ast2d->load(texFileName, false, false);
  + newLight->createChild("filename") = fileName.path() + hdrFileName;
  } else if (l.type == "sunSky") {
  newLight = createNode(lightName, l.type);
  if (l.sunSky.up.size()) {
  