Sets the major and minor version of OpenGL to request.
Setting major and minor to zero will use the default values.
Setting major and minor lower than the minimum versions required by GTK will result in the context choosing the
minimum version.
The this must not be realized or made current prior to calling this function.
| this |
a `GdkGLContext` |
| major |
the major version to request |
| minor |
the minor version to request |