Apply shadow only to the naturally lit part of the fragment color (#11722)

Apply shadow only to the naturally lit part of the fragment color (#11722)

Fragment color for nodes is now calculated from:

 * Texture color, highlighted by artificial light if present (light color conveyed via vertex color).
 * Texture color highlighted by natural light (conveyed via vertex color) filtered by shadow.
 * Reflected day/moonlight filtered by shadow (color and intensity), assuming some portion of the light is directly reflected from the materials.