Reland Refactor c10::complex and cleanup c10::Scalar (#39306)
Summary:
This reverts commit 8556664d6896a8e7f48f1c419e06e0568b9ee09e.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39306
Differential Revision: D21818096
Pulled By: albanD
fbshipit-source-id: ed4396fcad8c7036fb7bfa2f3da6ed63c0eb6625
