Add parameter types to the PFFF AST 2

Summary:
* This adds the content for `HintCallback` and updates its uses.
* This parses `...` as part of the syntax for
  callback parameter... parameters

Sending a separate diff because this is extra gnarly...

Test Plan:
existing unit tests; `pfff -dump-php` on something like

  <?hh
  // Copyright 2004-present Facebook. All Rights Reserved.

  function iAreTerriblePerson((function(?(int,int), string, ...): int) $dude) {
    return 5;
  }

and manually verify the glorious AST.

This depends on its predecessor, D691179

Reviewers: pad, amenghra, julienv

Reviewed By: pad

Differential Revision: https://phabricator.fb.com/D694323