Don't run user function until all UserRRefs in the args are confirmed (#34497)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34497
Use a thread_local table to intercept UserRRefs created during user
function args deserialization, and then wait for confirmations of
those UserRRefs before launching the given user function.
Differential Revision: D20347464
Test Plan: Imported from OSS
Pulled By: mrshenli
fbshipit-source-id: 087484a2d2f03fbfb156752ab25653f39b412a07
