DeriveFunctor: Check for last type variables using dataConUnivTyVars

Previously, derived instances of Functor (as well as the related classes Foldable, Traversable, and Generic1) would determine which constraints to infer by checking for fields that contain the last type variable. The problem was that this last type variable was taken from tyConTyVars. For GADTs, the type variables in each data constructor are not the same type variables as in tyConTyVars, leading to #22167 (closed).

This fixes the issue by instead checking for the last type variable using dataConUnivTyVars. (This is very similar in spirit to the fix for #21185 (closed), which also replaced an errant use of tyConTyVars with type variables from each data constructor.)

Fixes #22167 (closed).