Auto tupling of function parameters for generic tuples

As a generalization of `Tuple2[Int, Int]`, `Int *: Int *: Unit` should also allow autotupling.

```scala
val h2: Int *: Int *: Unit => Int = (x, y) => x + y
```
it currently fails with

```
4 |  val h2: Int *: Int *: Unit => Int = (x, y) => x + y
  |                                      ^^^^^^^^^^^^^^^
  |                                   wrong number of parameters, expected: 1
```