[X86][SSE] Don't fold shuffle(binop(),binop()) -> binop(shuffle(),shuffle())...

[X86][SSE] Don't fold shuffle(binop(),binop()) -> binop(shuffle(),shuffle()) if the shuffle are splats

rGbe69e66b1cd8 added the fold, but DAGCombiner.visitVECTOR_SHUFFLE doesn't merge shuffles if the inner shuffle is a splat, so we need to bail.

The non-fast-horiz-ops paths see some minor regressions, we might be able to improve on this after lowering to target shuffles.

Fix PR48823