Creates a new `GdkGLContext` for the `GdkSurface`.
The context is disconnected from any particular surface or surface. If the creation of the `GdkGLContext` failed, throws will be set. Before using the returned `GdkGLContext`, you will need to call [ method@Gdk.GLContext.make_current] or [method@Gdk.GLContext.realize].
this |
a `GdkSurface` |
the newly created `GdkGLContext` |