Add parameter types to the PFFF AST

Summary:
I'd like to have some of the fancier annotation types in the AST
so I can use them:

* Add tuples and nullable; propagate through pfff and make best-effort
  fixes wherever code `match`es on `hint_type`

* Stage 2 (to follow): add a type for callback type annotations

Test Plan: `make test`

Reviewers: pad, amenghra, julienv

Reviewed By: julienv

Differential Revision: https://phabricator.fb.com/D691179