Grabbing Qml scene does not set the QImage device pixel ratio

The generated image does not contains the window device pixel ratio property and lead to big images being painted while the grabbed window is on a retina screen and drawn on a non retina screen.
Those calls are affected:

• QQuickWindow::grabWindow()
• QQuickWidget::grabFramebuffer()

Workaround, set the image devicePixelRatio yourself:

• image.setDevicePixelRatio(QQuickWindow::effectiveDevicePixelRatio())
• image.setDevicePixelRatio(QQuickWidget::quickwindow::effectiveDevicePixelRatio())