which ensures we won't have inconsistent black-vs-isort errors
going forward. We can always format by running `ufmt format .`
at the root, and check with `ufmt check .` in our CI actions.
* Read install requirements from requirements.txt
* read extras_require from requirements-dev.txt
* add requirements-dev.txt to MANIFEST.in
* apply fixes for new version of Black and Flake8
* don't upgrade Pyre
* re-format
I noticed that the typed visitors codegen was creating messy types such as Union[SingleType]. We have a clean-up for Union[SingleType] snuck into gen_matcher_classes. So, lets remove that snuck-in clean-up from gen_matcher_classes and apply it globally to all codegen. This makes its purpose a lot more obvious, while helping decouple necessary codegen from prettifying/simplifying transforms. It also cleans up typed visitors, so that's a bonus.
