ONNX Update training ops and training amenable export API (#32950)
Summary:
- Update Dropout and Batchnorm in opset 12 : https://github.com/onnx/onnx/pull/2568
- Update api logic for exporting to ONNX training amenable models
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32950
Reviewed By: hl475
Differential Revision: D19710370
Pulled By: houseroad
fbshipit-source-id: e5e79d38552936966662c41d39ddf33be1ba3e35
