list types are inconsistent

list<ObjectType> is a QQmlListProperty which implicitly is a reference to some property or other actual storage

list<valueType> is a QList that's passed by value.

Passing by value is what we should do when compiling to C++, as determined by the whole value type saga. Therefore, we need a new container type for object types. The new container should be passed by value, too.

We can do this either by using a different type modifier, such as "sequence", or by introducing yet another pragma.