typing: add more type hints to the errors module These were found by looking for `Any` types in the generated `*.pyi` file after running the tests. There are some more complicated types that I'm not sure of, and am leaving untyped. I also can't figure out how to get `self.hint` to be anything other than `Any` in most classes. Differential Revision: https://phab.mercurial-scm.org/D11719