QMetaType: explicitly include qobject.h

convertMetaObject() function requires definition of QObject class,
but qobject.h is not included explicitly. Instead it is pulled by
qabstractitemmodel.h.

Include it explicitly to fix builds with -no-feature-itemmodel.

Change-Id: I4386375588c451262923501ab8dd7374c1f729ec
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 1d7e3ef77eccdea566bbb55f24267d70c8a1ebce)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qmetatype.cpp

@@ -5,6 +5,7 @@
 
 #include "qmetatype.h"
 #include "qmetatype_p.h"
+#include "qobject.h"
 #include "qobjectdefs.h"
 #include "qdatetime.h"
 #include "qbytearray.h"