Move complex extension test to c10 (#28208)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28208
Backend extensions should call torch::RegisterOperators, not globalATenDispatch().
If the op is still on globalATenDispatch, then torch::RegisterOperators will do the right thing and forward it to globalATenDispatch.
ghstack-source-id: 92436988
Test Plan: waitforsandcastle
Differential Revision: D17975369
fbshipit-source-id: 0d4bd5e4e5b86e6dcfba527a7d11c25508896ac1
