Backport Ordering equality and other improvements

Forward more methods for reverse orderings

Forward most comparison methods (not just abstract
ones) in default implementations of Ordering.reverse
and PartialOrdering.reverse.

Remove unnecessary overrides for FloatOrdering and
DoubleOrdering.

(cherry picked from commit 957a114)

Add equality for Orderings

(cherry picked from commit f1fb5c7)

Make IntOrdering.reverse a val.

partial cherry-pick of ed28bff)

Author: NthPortal