[display] hover fails on pattern matching "rest" arguments

Hover fails with "Not enough arguments" when hovering over the `_` here.

```haxe
class Main {
static function main() {
var f:Foo;
switch (f) {
case Bar(_):
}
}
}

enum Foo {
Bar(a:Int, b:Int);
}
```

It would be neat if it instead listed all the ignored arguments, but I'm not sure if that's possible with the current `DisplayItem` kinds.