Add `torch.flip{lr, ud}` (#38599)
Summary:
Reference: https://github.com/pytorch/pytorch/issues/38349
TODO:
* [x] Add Tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38599
Differential Revision: D21941884
Pulled By: mruberry
fbshipit-source-id: 7a442ff11051c2c868cf8e3c04e4bba0f1a1d426
