Apply consistent layout to type constructors in signatures

[neongreen]

Input:

f :: forall x y.
      D x y x y

Output:

f ::
  forall x y.
  D x y x
    y

---

While I'm at it, this should also probably be consistent with data declarations?

Input:

data D = forall x y.
         D x y x y

Output:

data D
  = forall x y.
    D
      x
      y
      x
      y

---

My preferred option in both cases would be:

f ::
  forall x y.
  D x y x y

data D
  = forall x y.
    D x y x y

[mrkkrp]

What do you mean "while I'm at it"? If you are referring to your current work on #423, then please introduce as few changes as possible and then when it's merged we can return to this one and do it in a separate PR.

Otherwise, yes, I agree that these changes make sense.

[neongreen]

"while I'm at it" means "while I'm talking about things that have D x y x y in them". Sorry for confusing you.

I'm not going to make this change in #423.