Add XHAST linter standards
Summary: Ref T8742. As mentioned in D13512. This still needs some work, but looks roughly how I expect it to. Mainly, I want to move the standards stuff to the linter itself rather than the linter rule. I wanted to push this out for some initial feedback though.
Test Plan: This still needs work.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin
Maniphest Tasks: T8742
Differential Revision: https://secure.phabricator.com/D13942