Brush for ReflectionProbe

[solitaryurt]

Would be sweet to be able to define ReflectionProbe using a brush with a particular texure.

We already define both: option_clip_texture_name and option_skip_texture_name, could add option_reflection_texture_name and define a ReflectionProbe, and set its size and transform based on the brush.

If all six faces have the texture, just process it, otherwise skip.