[DataPipe] Adding functional API for FileLister (#78419) (#78948)
Fixes #78263
Follow-up from pytorch/data#387. This adds a functional API `list_files()` to `FileListerDataPipe`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78419
Approved by: https://github.com/NivekT, https://github.com/ejguan
Co-authored-by: Robert Xiu <xiurobert@gmail.com>
