Use PhutilXHPASTBinary methods

Summary: Use PhutilXHPASTBinary methods instead of xhpast_parse functions. Depends on D11517.

Test Plan: N/A, this is a direct swap.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11612