Handle anonymous wild cards in type or data family instance declarations like
unnamed type variables. For instance (pun intented):
type family F (a :: *) (b :: *) :: * type instance F Int _ = Int
Is now the same as:
type family F (a :: *) (b :: *) :: * type instance F Int x = Int
Note that unlike wild cards in partial type signatures, no errors (or warnings
with -XPartialTypeSignatures) are generated for these wild cards, as there is
nothing interesting to report to the user, i.e. the inferred kind.
Only anonymous wild cards are supported here, named and extra-constraints wild
card are not.