vertexcodec: Reverse SIMD lookup tables
vertexcodec: Reverse SIMD lookup tables

Now that we no longer have the 1-bit case to decode, we can reverse the
tables instead of reversing the lookup mask; this makes SSE decoding
slightly faster.

Additionally this change reverts back to generating tables using code
but does it at static construction time instead.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer