[rpc] Switch RRef to be managed by intrusive_ptr (#33189)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33189
Add RRefInterface to Aten/Core, which will later be used by IValue
Switch all the rpc code base to use intrusive_ptr instead of shared_ptr,
so that we could add it to IValue.
Actual adding to IValue and JIT will be in next PR
Test Plan: Imported from OSS
Differential Revision: D19871241
Pulled By: wanchaol
fbshipit-source-id: d7e1fd04b46320e0f26c18591b49c92ad30a4032
