vertexjit: Optimize u8/u16 weights a little.

Only for uncommon values.
vertexjit: Initial u8/u16 weights for d3d9.
Oops, forgot to multiply.
vertexjit: Optimize the d3d9 weights a bit.

Only used without skinning on, or with morph, of course.
vertexjit: Use SSE for all weights, u8/u16.
vertexjit: Use SSE4 in tc u8/u16 code.

It's not much different for non-SSE 4, might as well be common.
Merge pull request #6917 from unknownbrackets/vertexjit

Add x86 weight ToFloat handling for d3d9