Include parentheses in n_ARRAY_VALUE_LIST node

Summary: Currently parsing array(1, 2, 3) results in a n_ARRAY_VALUE_LIST with a concrete string of 1, 2, 3. Compare this to list($x, $y) which results in a n_ASSIGNMENT_LIST with a concrete string of ($x, $y).

Test Plan: See next diff.

Reviewers: Blessed Reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D13858