text: Title: [Feature request] Use protobuf's generator to generate pyi stubs
  Body: ### Describe the feature
  
  It looks like protobuf now offers a native way for generating pyi files: https://github.com/protocolbuffers/protobuf/blob/main/python/README.md#implementation-backends. Currently in ONNX we use a custom script. The official tool has the potential to be more correct and robust.