Follow up on proto3 compatiblity. (#1799)
Follow up on proto3 compatiblity. (#1799)

This provides additional has_*() methods abstraction/replacement for proto3 compatibility.
microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime,microsoft/onnxruntime