Ordering[T] and friends should be contravariant #7179
Description
The Ordering[T] trait and its friends Equiv[T] and PartialOrdering[T] should be contravariant in T. This would for example allow SeqLike.sorted to be declared as:
def sorted(implicit ord: math.Ordering[A]): Reprrather than
def sorted[B >: A](implicit ord: math.Ordering[B]): ReprIt would also provide a good didactic example of contravariance in the library!