Add Unflatten Module (#41564)
Summary:
This PR implements a feature extension discussed in https://github.com/pytorch/pytorch/issues/41516.
I followed this other PR https://github.com/pytorch/pytorch/issues/22245 to add this other module. While I was at it, I also added `extra_repr()` method in `Flatten` which was missing.
I see there are no unit tests for these modules. Should I add those too? If so, what is the best place I should place these?
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41564
Reviewed By: gchanan
Differential Revision: D22636766
Pulled By: albanD
fbshipit-source-id: f9efdefd3ffe7d9af9482087625344af8f990943
