Optimize GlobeSurfaceShaderSet.getShaderProgram

For 3K fullscreen view of Mount Everest, it was `2.3%` to `2.5%` of the profile (one of the top hot-spots).

Now it is `~0.07%`.

@kring at this point, we might want to rename `GlobeSurfaceShaderSet` to something else and make it just a function.