Waits until the completion of every request.
If you call AsyncGPUReadbackRequest.done on any request after this call, it always returns
true whether the request completed successfully or not.
You can use AsyncGPUReadbackRequest.hasError to find out whether a request has been successful or not.
WaitAllRequests stalls both the GPU and the CPU. This means that calling this function results in a large performance decrease. Therefore, you should use this function sparingly.