Add Pytorch Native AMP support in Trainer (#6151)
Add Pytorch Native AMP support in Trainer (#6151)

* fixed type; add Pytorch Native CUDA AMP support

* reverted commit on modeling_utils

* confirming to HF black formatting rule

* changed bool value of _use_apex

* scaler support for gradient clipping

* fix inplace operation of clip_grad_norm

* removed not while version comparison
huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/pytorch-transformers