Tuple type arguments aren't left as multiline

[Niols]

As of f35eee4, Topiary formats:

type t =
  (
    int,
    float,
    string
  ) foo

as:

type t =
  (int, float, string) foo

The multi-line-ness of the type arguments is completely forgotten. When the type arguments are big, this can make for a nasty surprise, eg.

I'm not super happy with my snippet, so that might not be how things should look. But at least they shouldn't look as Topiary makes them look now!

To reproduce:

$ nix run github:tweag/topiary/f35eee4 -- format -l ocaml <<EOF
type t =
  (
    int,
    float,
    string
  ) foo
EOF