Use PHP type hinting in `ArcanistXHPASTLinter`.
Use PHP type hinting in `ArcanistXHPASTLinter`.

Summary: Explicitly specify the types of the function parameters.

Test Plan: `arc unit`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8388

julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist