clone method
Create a copy of this declaration, mainly used on class member inheritance and function arguments passing.
Implementation
@override
HTClassDeclaration clone() => HTClassDeclaration(
    id: id,
    classId: classId,
    closure: closure,
    source: source,
    genericTypeParameters: genericTypeParameters,
    superType: superType,
    implementsTypes: implementsTypes,
    withTypes: withTypes,
    isExternal: isExternal,
    isAbstract: isAbstract,
    isEnum: isEnum,
    isTopLevel: isTopLevel);