QMetaType: Add qHash() overload

This is needed for use in QHash and similar.
It's essentially the same as using the integer id, but typesafe

Change-Id: I9515b8e178c8f9828934cb0bb099cce5553ec393
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/kernel/qmetatype.cpp

@@ -3002,6 +3002,14 @@ static const QtPrivate::QMetaTypeInterface *interfaceForType(int typeId)
 */
 QMetaType::QMetaType(int typeId) : QMetaType(interfaceForType(typeId)) {}
 
+
+/*! \fn size_t qHash(QMetaType type, size_t seed = 0)
+    \relates QMetaType
+    \since 6.4
+
+    Returns the hash value for the \a type, using \a seed to seed the calculation.
+*/
+
 namespace QtPrivate {
 #if !defined(QT_BOOTSTRAPPED) && !defined(Q_CC_MSVC)
 

src/corelib/kernel/qmetatype.h

@@ -52,6 +52,7 @@
 #ifndef QT_NO_QOBJECT
 #include <QtCore/qobjectdefs.h>
 #endif
+#include <QtCore/qhashfunctions.h>
 
 #include <array>
 #include <new>
@@ -2536,6 +2537,13 @@ constexpr const QtPrivate::QMetaTypeInterface *const qt_incomplete_metaTypeArray
     QtPrivate::qTryMetaTypeInterfaceForType<Unique, T>()...
 };
 
+inline size_t qHash(QMetaType type, size_t seed = 0)
+{
+    // We cannot use d_ptr here since the same type in different DLLs
+    // might result in different pointers!
+    return qHash(type.id(), seed);
+}
+
 QT_END_NAMESPACE
 
 QT_DECL_METATYPE_EXTERN_TAGGED(QtMetaTypePrivate::QPairVariantInterfaceImpl,