RenderContext: OpenGL

[almarklein]

I'm pretty sure it's possible to obtain an OpenGL context from the windowId that the RenderCanvas provides for rendering to screen. With that, it would be possible to render to our canvases using OpenGL.

OpenGL is deprecated. It's unlikely that I will work on this myself. Just putting this idea out there, because there's plenty of OpenGL code around, so this would actually be useful. Not sure if a get_gl_context_from_window_id() could be part of rendercanvas. Maybe in utils?