Change vs_ibl_skybox.sc to correctly use radians instead of degrees when
specifying field-of-view. Additionally, use u_viewRect to find the correct
aspect ratio of the viewport, instead of hard-coding to 4/3.
Change fs_ibl_skybox.sc, fixing a number of small issues and mistakes. These
mistakes would lead to incorrect lighting results, especially with metallic
materials at glancing angles.
This commit does not include the rebuilt .bin output of shaderc for these
shaders.
