Fix specular render_mode for visual shaders

[Chaosus]

Seems like "disabled" specular render mode should be first in order to correct processing, this may change the specular modes for existed visual shaders, but this will fix schlick_ggx specular mode...
Fix #41525

PS. I think documentation is wrong and the default specular mode is "specular_disabled"

[clayjohn]

I am worried that there are other places that rely on the order of render modes to work properly.

Plus this change just makes it so that specular_mode_disabled can't be used.

[Chaosus]

Alright - I did it another way(less elegant but fully backward compatible):

[Chaosus]

@clayjohn recheck again

Plus this change just makes it so that specular_mode_disabled can't be used.

As I noted - It's used by default and can be omitted

[akien-mga]

Thanks!