Improve linter handling of short array syntax

Summary: Currently, linting PHP short array syntax (i.e. [...]) throws an exception ("Expected open parentheses"). This diff relaxes some restrictions which prevent short array syntax from linting with ArcanistParenthesesSpacingXHPASTLinterRule.

Test Plan: Modified test cases.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: agenticarus, Korvin

Differential Revision: https://secure.phabricator.com/D13895