nir: Add an LOD parameter to image_*_size

The OpenCL image_width/height/depth functions have variants which can take an LOD parameter. More importantly, LLVM-SPIRV-Translator always generates OpImageQuerySizeLod even if the LOD is guaranteed to be zero. Given that over half the hardware out there has an LOD field for image size queries (based on a rudimentary scan through their NIR -> whatever code), we may as well just add the source to the NIR intrinsic. If this is ever a problem for anyone, the lowering is pretty trivial.

I've also added asserts to everyone's drivers that should alert them if they ever see an LOD other than zero. This will never happen with GL or Vulkan so there's no need for panic.