add mutation support for forward_pre_hook and forward_hook (#22285)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22285
Previously forward hooks are expected to return None, this PR adds the support to overwrite input and output in `forward_pre_hook` and `forward_hook`, this is used to implement inserting quant/dequant function calls around forward functions.
Differential Revision: D16022491
fbshipit-source-id: 02340080745f22c8ea8a2f80c2c08e3a88e37253
