QDesktopServices: make QOpenUrlHandlerRegistry a non-QObject

It seems to have been a QObject solely for its single slot.

But since Qt 5, slots need no longer be defined on QObjects, so we can
remove the inheritance from QObject now. We still need a QObject as
the context object in connect(), but that can be just be an aggregated
naked QObject.

Saves 26 relocations, ~1.5KiB in TEXT and ~0.3KiB in DATA on optimized
GCC 11.2 Linux AMD64 C++20 builds.

Pick-to: 6.3 6.2
Change-Id: Ic45a8e892ec2bd5de5de8fbd32ec7a167c501803
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/gui/util/qdesktopservices.cpp

@@ -58,9 +58,8 @@
 
 QT_BEGIN_NAMESPACE
 
-class QOpenUrlHandlerRegistry : public QObject
+class QOpenUrlHandlerRegistry
 {
-    Q_OBJECT
 public:
     QOpenUrlHandlerRegistry() = default;
 
@@ -75,7 +74,8 @@ public:
     HandlerHash handlers;
 
 #if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
-public Q_SLOTS:
+    QObject context;
+
     void handlerDestroyed(QObject *handler);
 #endif
 
@@ -336,8 +336,8 @@ void QDesktopServices::setUrlHandler(const QString &scheme, QObject *receiver, c
     h.name = method;
     registry->handlers.insert(scheme.toLower(), h);
 #if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
-    QObject::connect(receiver, SIGNAL(destroyed(QObject*)),
-                     registry, SLOT(handlerDestroyed(QObject*)),
+    QObject::connect(receiver, &QObject::destroyed, &registry->context,
+                     [registry](QObject *obj) { registry->handlerDestroyed(obj); },
                      Qt::DirectConnection);
 #endif
 }
@@ -358,6 +358,4 @@ void QDesktopServices::unsetUrlHandler(const QString &scheme)
 
 QT_END_NAMESPACE
 
-#include "qdesktopservices.moc"
-
 #endif // QT_NO_DESKTOPSERVICES