WIP: Handle sigs in separate TyClGroups

Fixing #12088 implies that we put declarations and definitions in separate TyClGroups.

E.g. consider this example:

{-# LANGUAGE StandaloneKindSignatures #-} 

import Data.Kind

type X :: Type
data X

If the renamer puts type X :: Type and data X into separate TyClGroups, the type checker must be prepared to handle it.

• Before this patch, the type checker always assumed that signatures were put into the same TyClGroup as the definition.
• After this patch, no such assumption is made.