egl: pack all strips per gear into a single draw

We can pack multiple triangle-strips into a single draw, by inserting degenerate triangles between them. This should be a big win in terms of CPU usage.

To avoid inserting needless degenerate triangles to invert face-winding, we can manually invert the order of the back-face as well as emit the inner face last. This ensures every strip starts with the right face-winding.