This is a modified version of #9277, which was merged but then reverted later for performance reasons. The performance issues from #9177 have been fixed (`Linter` no longer creates a new map of rules whenever it lints text).

The goal of this change is to progress towards being able to remove the `rules` property from `Linter` instances. Unfortunately, this isn't possible yet, since there are a few other modules that rely on reading the list of defined rules.