I was investigating why GHC allocates so many `TyConApp` constructors and observed that the primary cause of allocation (25%) was `TyConApp Type []`. We should add a special case to `mkTyConApp` to check for this case and create a static top-level definition for `TyConApp Type []` so all these redundant constructors are not duplicated. I estimate this will reduce allocations when compiling `Cabal` by at least 30mb.