function bilinearInterpolate(tx, ty, h00, h10, h01, h11) {
  const a = h00 * (1 - tx) + h10 * tx;
  const b = h01 * (1 - tx) + h11 * tx;
  return a * (1 - ty) + b * ty;
}
Requests the tile's content.
<p>
The request may not be made if the Cesium Request Scheduler can't prioritize it.
</p>

@return {Promise<Cesium3DTileContent>|undefined} A promise that resolves when the request completes, or undefined if there is no request needed, or the request cannot be scheduled.
@private