[nnc] Add a API to unroll loops by a given factor (#72071)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/72071
Reviewed By: ngimel
Differential Revision: D33946250
Pulled By: navahgar
fbshipit-source-id: 3f3f92054174620025a9d71154d006f1738953e2
(cherry picked from commit d8b53598e92e8d2e050bc1d0cd070fbe8e2d77dd)
