Add binding for QOpenGLWidget (Qt 6)

[5k3105]

I have an application that used QOpenGLWidget and used QPainter to draw into it.

[mappu]

Yes - the 3D libraries are not yet part of the binding, it would be good to add them.

It will take some special care, since it would be out of scope for Miqt to generate bindings for all of OpenGL itself. After constructing the QOpenGLWidget it should be necessary to interoperate with another Go OpenGL binding.

This is a subproject of #58

[5k3105]

Btw, I switched from using a QGLWidget to a QWidget and it worked fine. Its just some 2D graph, so I guess it didn't need GL anyway.

[mappu]

#334 adds a minimal QOpenGLWidget for Qt 5, but it's not yet present for Qt 6. I'll reopen and retitle the issue for the remaining work.