[DataPipe] Add docstrings for IterDataPipe and MapDataPipe, along with small doc changes for consistency (#72618)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72618
The major changes are in torch/utils/data/dataset.py
Let me know if anything is unclear. I'm open to suggestion.
Test Plan: Imported from OSS
Reviewed By: VitalyFedyunin
Differential Revision: D34119492
Pulled By: NivekT
fbshipit-source-id: 358cb6d33d18501f9042431350f872ebaa9b4070
(cherry picked from commit 53b484f60ad942c9b86b060c40fe5a3b994424f9)
