Port register_string_ops.cpp to new operator registration API (#37008)
Summary:
Adresses https://github.com/pytorch/pytorch/issues/36925
We have a new operator registration API introduced in https://github.com/pytorch/pytorch/issues/36258, and we need to port all use sites of the old registration API to use it.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37008
Differential Revision: D21160557
Pulled By: jessebrizzi
fbshipit-source-id: 6bc0d57c40229cc7a477cde371c08479d4a4fe4f
