vertexcodec: Optimize vertex block transpose
vertexcodec: Optimize vertex block transpose

Change the order of operations to be able to first shuffle bytes and
shuffle dwords later; this results in a more optimal sequence since we
don't need intermediate byte-wise transpose of a single vector - instead
we need to change the order of resulting vectors which can be done
with minimal number of register moves.

The transpose still spills a lot on x86 but that's a given since there's
just not enough registers...

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer