Implements the orthogonal parametrization (#62089)
Summary:
Implements an orthogonal / unitary parametrisation.
It does passes the tests and I have trained a couple models with this implementation, so I believe it should be somewhat correct. Now, the implementation is very subtle. I'm tagging nikitaved and IvanYashchuk as reviewers in case they have comments / they see some room for optimisation of the code, in particular of the `forward` function.
Fixes https://github.com/pytorch/pytorch/issues/42243
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62089
Reviewed By: ezyang
Differential Revision: D30639063
Pulled By: albanD
fbshipit-source-id: 988664f333ac7a75ce71ba44c8d77b986dff2fe6
