Add clip_grad_norm_ to c++ api (#26140)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26140
Per https://github.com/pytorch/pytorch/issues/25883, we want to work
towards C++/Python API parity. This diff adds clip_grad_norm_ to the c++ API to
improve parity.
ghstack-source-id: 91334333
ghstack-source-id: 91334333
Test Plan: Added a unit test
Differential Revision: D17312367
fbshipit-source-id: 753ba3a4d084d01f3cc8919da3108e67c809ad65
