Add a linter rule for inline HTML

Summary: Ref T7409. Based on InlineHTMLSniff.

Test Plan: Added unit tests.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T9140, T7409

Differential Revision: https://secure.phabricator.com/D13871