[X86][SSE] combineX86ShufflesRecursively - add basic handling for combining...

[X86][SSE] combineX86ShufflesRecursively - add basic handling for combining shuffles of different widths (PR45974)

If a faux shuffle uses smaller shuffle inputs, try to recursively combine with those inputs directly instead of widening them immediately. Then widen all smaller inputs at the bottom of the recursion.

This will still mean we're generating nodes on the fly (PR45974) even if we don't combine to a new shuffle but it does help AVX2+ targets combine across xmm/ymm/zmm types, mainly as variable shuffles.