Adding functional way of stacking DataPipes with fixed mypy (#52885)
Summary:
Readding reverted PR with MyPY fixed
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52885
Reviewed By: ejguan
Differential Revision: D26676405
Pulled By: VitalyFedyunin
fbshipit-source-id: 020216c5522d21a4994cd896ae778c0b77f6444b
