Add support for explicitly marking a property as dirty

When a binding is backed by old-style property captures, then having
this API is needed for Qml.

Change-Id: Icf51efe057eaf845969ed2cda52d082dedde677e
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/corelib/kernel/qproperty.h

@@ -137,6 +137,8 @@ public:
 
     QMetaType valueMetaType() const;
 
+    void setDirty(bool dirty = true);
+
 private:
     explicit QUntypedPropertyBinding(const QPropertyBindingPrivatePtr &priv);
     friend class QtPrivate::QPropertyBase;

src/corelib/kernel/qpropertybinding.cpp

@@ -162,4 +162,11 @@ QMetaType QUntypedPropertyBinding::valueMetaType() const
     return d->metaType;
 }
 
+void QUntypedPropertyBinding::setDirty(bool dirty)
+{
+    if (!d)
+        return;
+    d->dirty = dirty;
+}
+
 QT_END_NAMESPACE