QMetaTypeModuleHelper: prevent slicing

Disable copy and move SMFs and make the dtor protected. This requires
to restore the default ctor, which in turn also becomes protected,
because it needn't be public.

Found by clazy-copyable-polymorphic.

Pick-to: 6.3
Change-Id: Ibde8202e755f6de05cd8f9e92cf0f9cf19b4e19b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qmetatype_p.h

@@ -76,6 +76,10 @@ QT_BEGIN_NAMESPACE
 
 class QMetaTypeModuleHelper
 {
+    Q_DISABLE_COPY_MOVE(QMetaTypeModuleHelper)
+protected:
+    QMetaTypeModuleHelper() = default;
+    ~QMetaTypeModuleHelper() = default;
 public:
     static constexpr auto makePair(int from, int to) -> quint64
     {