record DataCon : Type.name : DataCon -> Namename : DataCon -> Name.tag : DataCon -> Inttag : DataCon -> Int.arity : DataCon -> Natarity : DataCon -> NatgetCons : Defs -> NF vars -> Core (List DataCon)Given a normalised type, get all the possible constructors for that
type family, with their type, name, tag, and arity.
mkAlt : FC -> CaseTree vars -> DataCon -> CaseAlt varstagIs : Int -> CaseAlt vars -> Bool