Add instance for WrappedMonad

[treeowl]

Whenever https://github.com/ekmett/distributive/pull/52 lands, we can and presumably should add

instance (Representable m, Monad m) => Representable (WrappedMonad m) where
  type Rep (WrappedMonad m) = Rep m
  index (WrapMonad m) k = index m k
  tabulate f = WrapMonad (tabulate f)