In order to use Codex PHP inside of MediaWiki, we need to add it to the mediawiki/vendor repo (it can't just be installed using composer require).
For more details see: https://www.mediawiki.org/wiki/Manual:External_libraries
T379800 has been filed to request a security review (which will mostly concern this library's 3rd-party dependencies).
Acceptance Criteria
- The security review requested at T379800 is complete
- Any necessary changes from the security review have been addressed
- Update mediawiki/vendor to add wikimedia/codex at the latest version (currently 0.2.0)
- Update MW core's composer.json file to match