Unify fetching RRefs (#57859)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57859
Just like with assigning OwnerRRefs, we can also deduplicate the code paths for fetching their values. In fact this was duplicated three times, with different ways of post-processing the value (once for JIT, once for Python, once for autograd). Thanks to future, we can have that logic once, and then connect it to different follow-up steps.
ghstack-source-id: 129567050
Test Plan: CI
Reviewed By: mrshenli
Differential Revision: D28286172
fbshipit-source-id: e0742a99cf555755e848057ab6fee5285ff0df2a
