[ONNX] Add warning in ONNX export when constant folding is on in training-amenable mode (#40546)
Summary:
This PR introduces a warning when user tries to export the model to ONNX in training-amenable mode while constant folding is turned on. We want to warn against any unintentional use because constant folding may fold some parameters that may be intended to be trainable in the exported model.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40546
Reviewed By: hl475
Differential Revision: D22310917
Pulled By: houseroad
fbshipit-source-id: ba83b8e63af7c458b5ecca8ff2ee1c77e2064f90
