[display] @signature with function argument

Request the `@signature` at the single `(` here returns the signature of `sort()`, even though it's inside of a function declaration (vshaxe always requests the signature on `(` or `,`).

```haxe
class Main {
public static function main() {
var list:Array = [];
list.sort(function(a, b) {
(
return 0;
});
}
}
```

```
haxe --display Main.hx@115@signature
```