Fix major space-leak in GHC terms and tycon loading code

Changed Circular: TyCon -> DataCon -> Type -> TyCon
Into Flat: TyCon -> DataCon -> Type -> TyConName
In combination with a HashMap TyConName TyCon

This enabled the removal of a lazy Reader+State monad function
in the GHC2Core module which was retaining all the module information
loaded by the GHC API.

Reduced Space Usage by hundreds of MBs