[rpc][jit] support rpc_sync in TorchScript (#43043)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43043
This add the support for rpc_sync in TorchScript in a way similar to
rpc_async
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D23252039
Pulled By: wanchaol
fbshipit-source-id: 8a05329cb8a24079b2863178b73087d47273914c
