Add test for callable parameters with type parameters

This part of #108 actually already works, since parameters don’t have
their own node type: They’re AttributeDeclarations or
MethodDeclarations, and MethodDeclarations of course already support
type parameters.

test-samples/higherTypes.ceylon

@@ -2,3 +2,4 @@ interface SecondOrder<Box>
         given Box<Value> {
     shared formal Box<Float> createBox(Float float);
 }
+void takesCallableParamWithTypeParam(T f<T>(T t)) {}