Share nullary TyConApps

While looking at ticky profile of I have noticed that GHC allocates a great deal of types of the form TyConApp tycon []. In #17958 (closed) we optimised the specific case of liftedTypeKind, but profiles suggest that other types may also benefit from this treatment. The idea here is that we would modify TyCon to carry such a nullary TyConApp which would be used by mkTyConTy and mkTyConApp tc []. This helps compiler performance in a few ways:

• we avoid allocating, eliminating code and reducing GC pressure
• we reduce residency, lowering GHC's memory footprint and reducing cache pressure