Add constants and class methods to php_compat_info.json.

Summary: Allows the ArcanistXHPASTLinter to determine whether constants can be used, based on the target PHP version. Also added class methods to the compatibility information, although this isn't used yet (it is small anyway).

Test Plan: Created a test file that contained the JSON_PRETTY_PRINT constant. Verified that a linter error was raised.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9571