[Scala 3] Extra instances for Covariant, Invariant

[TimWSpence]

For scala 3, we should hopefully be able to support additional derived instances of Invariant and Covariant for nested type constructors. Specifically:

(Invariant[F], Functor[G]) => Invariant[[x] =>> F[G[x]]]
(Invariant[F], Contravariant[G]) => Invariant[[x] =>> F[G[x]]]
(Contravariant[F], Functor[G])=> Contravariant[[x] =>> F[G[x]]]

[joroKr21]

But both Functor and Contravariant are Invariant which composes.
Why do we need special instances for them?