Add Module::replace_module to C++ api (#22546)
Summary:
This adds a replace_module method to the C++ api. This is needed to be able to replace modules.
The primary use case I am aware of is to enable finetuning of models.
Given that finetuning is fairly popular these days, I think it would be good to facilitate this in the C++ api as well.
This has been reported by Jean-Christophe Lombardo on the [forums](https://discuss.pytorch.org/t/finetuning-a-model-on-multiple-gpu-in-c/49195).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22546
Differential Revision: D16440289
Pulled By: yf225
fbshipit-source-id: c136f914b8fc5c0f1975d877ea817fda5c851cda
