Front-end: Fix: Cubemap arrays only use 3-component coord when accessed as an image.

Front-end: Fix: Cubemap arrays only use 3-component coord when accessed as an image.

4 components are needed when used a texture, but not an image, which multiplies
layers and faces into the same coordinate.  This fixes it from using 4 everywhere,
to only using 4 for textures and 3 for images.