Allow to create local RRef with value (#28948)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28948
Add the constructor RRef(value) in python. This allows to wrap a local object with RRef an pass or return this RRef to users.
This enables returning, for example, a list of RRefs containing the parameters of a module to the user of the module.
ghstack-source-id: 93565010
Test Plan: unit test.
Differential Revision: D18241227
fbshipit-source-id: b9e9b958f40623348d62ee6fc9e7f0414b4215b7
