Give MonadTrans a QuantifiedConstraints superclass

[Henning Thielemann]

On Wed, 2 Jun 2021, Zemyla wrote:

> I feel like instead, MonadTrans should have a function
> (>>==) :: Monad m => t m a -> (a -> t m b) -> t m b
> 
> That way, it can prove it's a Monad while still staying Haskell 98.

I prefer that.