Add the ability to render a equiangular cube map single face as described in
https://blog.google/products/google-ar-vr/bringing-pixels-front-and-center-vr-video/
This was added as I found rendering directly in panorama space caused artefacts in denoising as the denoising occurs in 2D space.
Direct 6 cube faces rendering works with custom denoising, but I wanted slightly more quality.