Expose QOpenGLPaintDevice in Qt for Python

The class QOpenGLPaintDevice is available in Qt5 and PyQt5, but not in PySide2.

{{>>> from PySide2.QtGui import QOpenGLPaintDevice
ImportError: cannot import name 'QOpenGLPaintDevice'}}

The absence of class QOpenGLPaintDevice is documented at https://wiki.qt.io/Qt_for_Python_Missing_Bindings but it's still, you know, a bug. So it deserves to be registered on this tracker. Specifically, my personal interest in getting this one class exposed is to be stressed.

Background: In my case I'm trying to faithfully translate from C++ into python the working Qt virtual reality demo here https://github.com/ValveSoftware/openvr/blob/master/samples/helloworldoverlay/openvroverlaycontroller.cpp#L180

but I'm stumbling on this missing class, as I explained in my stackoverflow question here: https://stackoverflow.com/q/56945217/146574

I'd especially like to see the QOpenGLPaintDevice(QSize) constructor exposed.