Add RRef.local_value() for TorchScript (#35433)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35433
Make RRef TorchScript API the same as RRef Python API.
Differential Revision: D7923050
fbshipit-source-id: 62589a429bcaa834b55db6ae8cfb10c0a2ee01ff
