horizon_min horizon_max: two spherical angles, defining portion of sphere to emit light from.
Default is 0 90, which is upper hemisphere. -90 90 will be whole sphere.
sample_color: Default = 1: sample color of each individual light from skybox images, if they are present.
0: use shader color, set by q3map_lightRGB/q3map_lightImage/_up skybox image/qer_editorImage.
* q3map_skylight may be used multiple times in a single shader
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