Improve test data format for XHPAST unit tests
Summary: Instead of having the input data and expected output stored in separate files, combine all data into a single file format similar to the *.lint-test format.
Test Plan: Ran unit tests.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D14500