Add mechanism for functorch to error out on autograd.Function (#71866)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71866
See title. There is a minimal perf regression for the non-functorch case
(a TLS access and a null check).
Test Plan: Imported from OSS
Reviewed By: soulitzer
Differential Revision: D33825279
Pulled By: zou3519
fbshipit-source-id: afa2ad5a672cc9225d2bb6b46ee7f3f1513c1e02
(cherry picked from commit 17ae1d3e9dcf57193a2d90f755e18994671c9f13)
