[NCCL] Support NCCL Send/Recv (#44921)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44921
This diff adds support for Process Group point-to-point operations on NCCL backend based on ncclSend/ncclRecv. See https://github.com/pytorch/pytorch/issues/43995 for more context.
ghstack-source-id: 113592785
Test Plan: unittest
Reviewed By: jiayisuse
Differential Revision: D23709848
fbshipit-source-id: cdf38050379ecbb10450f3394631317b41163258
