Bug: Printer fails to write generics for superclasses after setting it

```java
@Test
void test() {
CtType type = Launcher.parseClass("class Foo {}");
CtType foo = type.getReference().getTypeDeclaration();
type.setSuperclass(foo.getReference());
List typeParameters = type.getSuperclass().getTypeDeclaration().getFormalCtTypeParameters(); // has size 1
String printedClass = type.toString(); // drops the generic type on the extended class. output: "class Foo extends Foo {}"
}
```
The example above shows the problem. The expected output is `class Foo extends Foo {}` but currently the printer drops the generic type. After some debugging I found something, that could be the problem:
[ElementPrinterHelper](https://github.com/INRIA/spoon/blob/e8a1596aa29d8d34f84087fb0dbce1d032b2259f/src/main/java/spoon/reflect/visitor/ElementPrinterHelper.java#L250) `final Collection> arguments = ctGenericElementReference.getActualTypeArguments();`returns an empty list.
This looks like not a printer related problem, but more like a problem in setting a generic super class. Did I miss some method for setting a generic superclass explicitly with parameters? The type parameters for the super class are strangely correct in the model.