Allow ArcanistPhutilXHPASTLinter to be configured from .arclint.

Summary: Currently, PhabricatorLintEngine configures the ArcanistPhutilXHPASTLinter linter. In order to use .arclint instead, we need to expose the ArcanistPhutilXHPASTLinter configuration to the .arclint format.

Test Plan: See D9064.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T2039

Differential Revision: https://secure.phabricator.com/D9066