GitLab

Summary:
Extract from https://github.com/pytorch/audio/issues/2419. Move the `FileObj` definition to dedicated file, so that it can be reused from files other than StreamReader.

Pull Request resolved: https://github.com/pytorch/audio/pull/2427

Reviewed By: carolineechen

Differential Revision: D36794367

Pulled By: mthrok

fbshipit-source-id: 999658f3f4d833566d933c9223e7a5d49d300574