[WIP][DataLoader] Prototype of SamplerIterableDataset (#49363)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/49363
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D25623637
Pulled By: ejguan
fbshipit-source-id: 9155d27d1fc91996b74110795cc73f1da0eedd44
