Make `SpirvValue`(`Kind`) representation and operations more orthogonal and robust (lossless).#348

eddyb wants to merge 6 commits intoRust-GPU:mainRust-GPU/rust-gpu:mainfrom

LykenSol:robust-spirv-value-zombiesLykenSol/rust-gpu:robust-spirv-value-zombiesCopy head branch name to clipboard