Replace references to _DataLoaderIter with _BaseDataLoaderIter (#27105)
Summary:
Back in April, malmaud added type annotations for `dataloader.py`. However, at about the same time, SsnL in https://github.com/pytorch/pytorch/issues/19228 replaced `_DataLoaderIter` with `_BaseDataLoaderIter` and two subclasses, `_SingleProcessDataLoaderIter`, and `_MultiProcessingDataLoaderIter`. However - probably because these changes happened in parallel at roughly the same time, the type stubs and several other references in the codebase were never updated to match this refactoring.
I've gone ahead and done the updates to reflect the refactoring in https://github.com/pytorch/pytorch/issues/19228, which fixes the specific type stub/impelementation mismatch pointed out in https://github.com/pytorch/pytorch/issues/26673, although not the broader problem that pytorch doesn't have a test to make sure that the `.pyi` type stub files match the real API defined in `.py` files.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27105
Differential Revision: D17813641
Pulled By: ezyang
fbshipit-source-id: ed7ac025c8d6ad3f298dd073347ec83bb4b6600c