Make c10::ComplexHalf a template specialization of c10::complex (#37426)
Summary:
This PR basically makes `c10::ComplexHalf` a template specialization of `c10::complex`. Since `c10::ComplexHalf` is not used much, this does not include much change.
Due to the fact that `c10::Half` does not have much `constexpr` methods, it is impossible to keep the same API. Currently, we are just completely reusing the old implementation. It is just the name getting changed from `c10::ComplexHalf` to `c10::complex<c10::Half>`. We can always change the implementation in the future when needed. But for now, I think this is OK.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37426
Differential Revision: D21300754
Pulled By: anjali411
fbshipit-source-id: fc0f65adccf97025a727735096780ce8078675a1
