[X86][AVX] Fold CONCAT(HOP(X,Y),HOP(Z,W)) -> HOP(CONCAT(X,Z),CONCAT(Y,W)) for float types

We can now enable this for AVX1 targets can now assist with canonicalizeShuffleMaskWithHorizOp cleanup.

There's still a few missed opportunities for merging subvector insert/extracts into shuffles, but they shouldn't cause any regressions now.