Make RecordFunction more robust for async use cases (#34122)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34122
Earlier work added support for async rpc cases when RecordFunction's
end callbacks might be called in a different thread; in addition some
extra care was needed to handle pointer to parent function;
This PR makes RecordFunction aware of potentially multiple threads in
use, as well as removes unused parent() call and restricts current()
RecordFunction to scope-based record functions (RECORD_FUNCTION macro)
Test Plan: unit tests
Differential Revision: D20297709
Pulled By: ilia-cher
fbshipit-source-id: 46a59e1b2eea0bbd8a59630385e193b38d30f9d1
