QWidget::mapTo/FromGlobal not symmetrical for widget embedded into QGraphicsView embedded with transform

Unearthed by commit: "Fix global coordinate mapping for child widgets in QGraphicsView". 56aad2ad6074237537fecf10d0cda0f3872e7f71 https://codereview.qt-project.org/#/c/114591/ (QTBUG-41135).

Launch example:

• Move slider

  ### on_pushButton_clicked QPushButton(0x1e50560, name="innerButton")
  ### on_pushButton_clicked mapToGlobal QPoint(473,267) back QPoint(8,10)
  ### on_pushButton_clicked QPushButton(0x1e50560, name="innerButton")
  ### on_pushButton_clicked mapToGlobal QPoint(473,267) back QPoint(8,10)
  

  ### MainWindow::on_pushButton_clicked QPushButton(0x22595b0, name="outerButton")
  >
  QWidget::mapToGlobal > QPushButton(0x22595b0, name="outerButton") QPoint(0,0)
  QWidget::mapToGlobal loop= QWidget(0x2231a30, name="outerLayoutWidget") 100 50
  QWidget::mapToGlobal QWidget(0x2231a30, name="outerLayoutWidget") pos= 100 50
  QWidget::mapToGlobal sc= QPointF(100,50)
  QWidget::mapToGlobal vp= QPoint(243,88)
  QWidget::mapToGlobal > QWidget(0x22592a0) QPoint(243,88)
  QWidget::mapToGlobal loop= QGraphicsView(0x2231800, name="outerGraphicsView") 244 89
  QWidget::mapToGlobal loop= QWidget(0x22316b0, name="central") 255 126
  QWidget::mapToGlobal loop= MainWindow(0x29fd50, name="MainWindow") 255 126
  QWidget::mapToGlobal r= QPoint(455,176)
  ><
  QWidget::mapFromGlobal > QPushButton(0x22595b0, name="outerButton") QPoint(455,176)
  QWidget::mapFromGlobal loop= QWidget(0x2231a30, name="outerLayoutWidget") 355 126
  QWidget::mapFromGlobal QWidget(0x2231a30, name="outerLayoutWidget") pos= 355 126
  QWidget::mapFromGlobal > QWidget(0x22592a0) QPoint(355,126)
  QWidget::mapFromGlobal loop= QGraphicsView(0x2231800, name="outerGraphicsView") 354 125
  QWidget::mapFromGlobal loop= QWidget(0x22316b0, name="central") 343 88
  QWidget::mapFromGlobal loop= MainWindow(0x29fd50, name="MainWindow") 343 88
  QWidget::mapFromGlobal vp= QPoint(143,38)
  QWidget::mapFromGlobal sc= QPointF(13.0435,6.95652)
  QWidget::mapFromGlobal r= QPoint(13,7)
  <
  ### MainWindow::on_pushButton_clicked mapToGlobal= QPoint(455,176) mapFromGlobal= QPoint(13,7)