Fix "normal geometry" not being restored

When restoring a maximized window, calling QWidget::showNormal()
on it wouldn't set it's previous non-maximized size.

QWidget::normalGeometry() doesn't have a setter, so use private API.

src/private/widgets/QWidgetAdapter_widgets_p.h

@@ -103,6 +103,7 @@ protected:
     void mouseMoveEvent(QMouseEvent *) override;
     void mouseReleaseEvent(QMouseEvent *) override;
     void closeEvent(QCloseEvent *) override;
+    virtual void setNormalGeometry(QRect);
 
     virtual bool onResize(QSize newSize);
     virtual void onLayoutRequest();