[pytorch] factor out return_names api (#47437)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47437
Test Plan: Imported from OSS
Reviewed By: bhosmer
Differential Revision: D24808213
Pulled By: ljk53
fbshipit-source-id: 8ec6d58952fd677ab2d97e63b060cafda052411a
