async function waitForRootLoaded(tileset, scene) {
  scene.renderForSpecs();
  const root = tileset.root;
  await pollToPromise(() => {
    scene.renderForSpecs();
    return root.contentFailed || root.contentReady;
  });
}
Wait until the root tile of the given tileset is loaded

@param {Cesium3DTileset} tileset The tileset
@param {Scene} scene The scene