Add PHPAST tests for static class expressions, callable, traits, finally and short array syntax

Summary: Ref T4334. These are all failing, but should pass. They pass with `php -l` on modern PHP.

Test Plan: Ran unit tests.

Reviewers: btrahan, Firehed

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4334

Differential Revision: https://secure.phabricator.com/D8030