Integrate monomorphization into Checker

[nponeccop]

If a polymorphic definition is used only monomorphically (e.g. id x = x is only fed ints) its @definitionType should be int->int and not forall a . a -> a.

Note that function monomorphization can be applied to individual arguments. E.g. apply f x = f x can be monomorphized in x but not in f, e.g. (int -> a) -> int -> a