QmlDesigner: Center on item on initialize

Change-Id: Ib68c2b1a651497f9092d390b1a5b3a59c85d21ce
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Henning Gründl <henning.gruendl@qt.io>

src/plugins/qmldesigner/components/formeditor/formeditorwidget.cpp

@@ -357,6 +357,7 @@ void FormEditorWidget::initialize()
             defaultZoom = m_formEditorView->rootModelNode().auxiliaryData("formeditorZoom").toDouble();
     }
     m_graphicsView->setZoomFactor(defaultZoom);
+    m_graphicsView->centerOn(m_formEditorView->scene()->rootFormEditorItem());
     m_zoomAction->setZoomFactor(defaultZoom);
     updateActions();
 }