Discourage references to `ActiveRecord::Associations::CollectionProxy` and other synthetic constants

[KaanOzkan]

We have some synthetic constants generated by tapioca that shouldn't be referenced in signatures. These won't exist at runtime and even if they are used with T::Sig::WithoutRuntime.sig runtime checks for that method is disabled which isn't preferred.

• ActiveRecord::Associations::CollectionProxy
• Constants from Tapioca::Dsl::Compilers::ActiveRecordRelations