[DataLoader] Rename files of functional datapipes (#51880)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51880
Using the reference of [iter-tools](https://more-itertools.readthedocs.io/en/stable/api.html) to rename files based on the functionality.
Test Plan: Imported from OSS
Reviewed By: VitalyFedyunin
Differential Revision: D26314776
Pulled By: ejguan
fbshipit-source-id: e97bac047a0fa808676cd6f3a9202109d17f81ca
