[Reland][DDP Communication Hook] Rename 4 Methods of GradBucket Class (#62592)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62592
Reland #62510
`GradBucket` is an important class defined in both C++ and Python, used for PyTorch Distributed Training. We need to rename the following methods for simplicity:
1) get_index -> index
2) is_the_last_bucket_to_allreduce -> is_last,
3) get_per_parameter_tensors -> gradients,
4) get_model_params_for_bucket -> parameters.
ghstack-source-id: 134848352
Test Plan: unit test
Reviewed By: andwgu
Differential Revision: D30049431
fbshipit-source-id: 1bcac331aa30e529b7230e3891bc811c531b0ea9
