PyRRef.owner() to return WorkerInfo (#28909)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28909
This allows to chain calls on RRef as exemplified in the new test case added.
ghstack-source-id: 92996018
Test Plan: unit test.
Differential Revision: D18231081
fbshipit-source-id: deeac044ef6d63f18ea241760ac17a3e644cb3d7
