[JIT] add support for torch.jit.Final in python 3.6 (#47393)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47393
Test Plan: Imported from OSS
Reviewed By: bdhirsh
Differential Revision: D24739402
Pulled By: Lilyjjo
fbshipit-source-id: 46f003f0a4b1a36894050b72b8f2334c30268e54
