[ONNX] Optimize export_onnx api to reduce string and model proto exchange (#44332)
Summary:
Optimize export_onnx api to reduce string and model proto exchange in export.cpp
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44332
Reviewed By: bwasti, eellison
Differential Revision: D23880129
Pulled By: bzinodev
fbshipit-source-id: 1d216d8f710f356cbba2334fb21ea15a89dd16fa
