Add repr to StreamWrapper (#66880)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66880
Help to print out `fileobj`
Test Plan: Imported from OSS
Reviewed By: NivekT
Differential Revision: D31764431
Pulled By: ejguan
fbshipit-source-id: 668a8fbe0078196d4d584be3dfb413c8ad5e72b1
