Support List[str].index (#39210) (#40348)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/40348
Test Plan: Imported from OSS
Reviewed By: wanchaol
Differential Revision: D22757035
Pulled By: firstprayer
fbshipit-source-id: 4fadf8beabf8d5bdfa5b0a185075f7caf9ba8b02
