[X86][AVX512] Fold not(kmov(x)) -> kmov(not(x)) and not(widen_subvector(x)) ->...

[X86][AVX512] Fold not(kmov(x)) -> kmov(not(x)) and not(widen_subvector(x)) -> widen_subvector(not(x))

Improve AVX512 mask inversion, rG38c799bce801 exposed some missing opportunities to move scalar not() back onto the boolvector types for folding with setcc etc.