[X86] lowerShuffleWithVPMOV - support direct lowering to VPMOV on VLX targets

[X86] lowerShuffleWithVPMOV - support direct lowering to VPMOV on VLX targets

lowerShuffleWithVPMOV currently only matches shuffle(truncate(x)) patterns, but on VLX targets the truncate isn't usually necessary to make the VPMOV node worthwhile (as we're only targetting v16i8/v8i16 shuffles we're almost always ending up with a PSHUFB node instead). PACKSS/PACKUS are still preferred vs VPMOV due to their lower uop count.

Fixes the remaining regression from the fixes in rG293899c64b75