QmlDesigner: Fix url property path resolving

Converting file:// urls to relative paths assumed that the file://
url would always point to a file that is in same or child folder of
the qml document, which broke for urls that pointed under generated
components folder.

Fixes: QDS-12029
Change-Id: I352ba01650ebf6c1c5fedef9323bf27b44491736
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Shrief Gabr <shrief.gabr@qt.io>
Reviewed-by: Qt CI Patch Build Bot <ci_patchbuild_bot@qt.io>
(cherry picked from commit 6cec311c5d)

src/tools/qml2puppet/qml2puppet/instances/objectnodeinstance.cpp

@@ -7,6 +7,7 @@
 #include <qmlprivategate.h>
 
 #include <QDebug>
+#include <QDir>
 #include <QEvent>
 #include <QQmlContext>
 #include <QQmlError>
@@ -627,8 +628,8 @@ QVariant ObjectNodeInstance::property(const PropertyName &name) const
             return QVariant();
 
         if (url.scheme() == "file") {
-            int basePathLength = nodeInstanceServer()->fileUrl().toLocalFile().lastIndexOf('/');
-            return QUrl(url.toLocalFile().mid(basePathLength + 1));
+            QFileInfo fi{nodeInstanceServer()->fileUrl().toLocalFile()};
+            return QUrl{fi.absoluteDir().relativeFilePath(url.toLocalFile())};
         }
     }