[Reland] [DDP] Implement a hook which performs FunctionalSGD step. (#62177)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62177
Reland of https://github.com/pytorch/pytorch/pull/61678
Fix CI failure by gating including torchvision model on whether torchvision is available or not.
ghstack-source-id: 134282165
Test Plan: CI
Reviewed By: SciPioneer
Differential Revision: D29904101
fbshipit-source-id: 47e799eb4a90acbbda91c5857ea00de3045d49f5
