QMetaContainer: add missing #include <iterator>

For std::iterator_traits, tags, std::advance, std::distance, etc.

Pick-to: 6.2 6.5 6.6
Fixes: QTBUG-114583
Change-Id: I443cf0c8a76243eead33fffd1768e904ae823f75
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/kernel/qmetacontainer.h

@@ -8,6 +8,8 @@
 #include <QtCore/qflags.h>
 #include <QtCore/qglobal.h>
 
+#include <iterator>
+
 QT_BEGIN_NAMESPACE
 
 class QMetaType;