Changed deriving of Functor, Foldable, Traversable to fix #7436. Added foldMap to derived Foldable instance.

The derived instances will no longer eta-expand the function. I.e. instead of
    fmap f (Foo a) = Foo (fmap (\x -> f x) a)
we now derive
    fmap f (Foo a) = Foo (fmap f a)

Some superflous lambdas are generated as a result. For example
    data X a = X (a,a)
    fmap f (X x) = (\y -> case y of (a,b) -> (f a, f b)) x
The optimizer should be able to simplify this code, as it is just beta reduction.

The derived Foldable instance now includes foldMap in addition to foldr.