Compatibility with QtWidgets.QOpenGLWidget vs QtOpenGLWidgets.QOpenGLWidget

[dalthviz]

I think we could keep this (the new QtOpenGLWidgets module in Qt6) but we need to do also the compatibility import at QtWidgets.py in a similar fashion as done with PySide6:

qtpy/qtpy/QtWidgets.py

Line 23 in 32f4a9f

from PySide6.QtOpenGLWidgets import QOpenGLWidget

What do you think @ccordoba12 ?

Originally posted by @dalthviz in #255 (comment)

[ccordoba12]

I agree with adding the equivalent line for PyQt6. That's a good idea because it avoids us to add another module to qtpy (i.e. QtOpenGLWidgets) just for a single widget.