[UPDATED] Add missing Monad instances to tuples

[Henning Thielemann]

On Sun, 7 Apr 2019, Fumiaki Kinoshita wrote:

> They are writer monads for sure, but WriterT does not subsume them. If a typeclass method has type Writer w a, it
> does not allow GeneralizedNewtypeDeriving on it due to the type roles.
> 
> I don't really have any idea how instance warnings should look like.

https://gitlab.haskell.org/ghc/ghc/issues/11796