[x86] Teach the new v4i32 shuffle lowering some more tricks to recognize
vzext patterns and insert-element patterns that for SSE4 have dedicated
instructions.

With this we can enable the experimental mode in a regression test that
happens to cover some of the past set of issues. You can see that the
new logic does significantly better here on the floating point cases.

A follow-up to this change and the previous ones will hoist the logic
into helpers so it can be shared across element type sizes as in this
particular case it generalizes cleanly.