[Gradient Compression] Add an index field to GradBucket for PowerSGD (#48757)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48757
Add an index field to GradBucekt, so error_dict is keyed by this index instead of the hashcode of input tensor. The replacement will be done in a separate diff, as the definition of this new method somehow couldn't be recognized in the OSS version.
Original PR issue: Investigate Applying PowerSGD to Communication Hook for Gradient Compression #47202
ghstack-source-id: 117939208
Test Plan: buck test mode/dev-nosan caffe2/test/distributed:c10d -- test_powerSGD_ddp_comm_hook_nccl
Reviewed By: rohan-varma
Differential Revision: D25288496
fbshipit-source-id: 6f71977809690a0367e408bd59601ee62c9c03ea
