* Add typedef declaration space, unify typedef name gathering, strengthen errorUnusedLocal
* Bonus round: make jsdoc presence way mroe typesafe
* Be exhaustive in nameForNamelessJSDocTypedef
* Remove nonrequired casts
* Replace more casts with guards
* Cannot be internal
* Debug.fail returns never, assert never no longer needs unreachable throw to satisfy checker
* Rename type
* Add replacement message as in 18287
