Hide directives when their uses are hidden

[rmosolgo]

Fixes #4882

This adds some hiding of directives when their uses are hidden. It only checks "one level" deep. Directives are hidden if:

• They aren't registered to the schema with directive(...) configurations
• AND no types with field(...) configurations using the directive are visible
• AND no resolvers and fields with argument(...) configurations using the directive are visible
• AND no enums with value(...) configurations using the directive are visible

It doesn't do recursive checking, so if a type is hidden because fields using it are hidden, then the directive will still be visible. Maybe that's possible but I'm guessing that adding visible? implementations to the app is a less complicated solution in that case.