Add a PHPAST test case for most of the PHP grammar

Summary: Ref T4334. This test case covers most of the common PHP grammar rules. It's not exhastive and avoids some of the tricky parts, but provides a wide base of rule tests.

Test Plan: Examined parse manually in PHPAST web tool. Ran unit tests.

Reviewers: btrahan, Firehed

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4334

Differential Revision: https://secure.phabricator.com/D8028