Make plugins compatible to latest KPluginFactory code
That one uses std::is_constructible<impl, QObject *, const QVariantList &> which will fail for our current plugin constructors due to being private and with only friend class KPluginFactory.
That one uses std::is_constructible<impl, QObject *, const QVariantList &> which will fail for our current plugin constructors due to being private and with only friend class KPluginFactory.