Implement PinchHandler.pinchOrigin

    Q_PROPERTY(PinchOrigin pinchOrigin READ pinchOrigin WRITE setPinchOrigin NOTIFY pinchOriginChanged)

    enum PinchOrigin {
        FirstPoint, PinchCenter, TargetCenter
    };

/*!
    \qmlproperty real QtQuick::PinchHandler::pinchOrigin

    The point to be held in place, around which the \l target is scaled and
    rotated.

    \value FirstPoint
        the first touch point, wherever the first finger is pressed
    \value PinchCenter
        the centroid between all the touch points at the time when the
        PinchHandler becomes \l active
    \value TargetCenter
        the center of the \l target
*/