Replace unsigned extract lane followed by sign extend
as added here https://chromium-review.googlesource.com/c/v8/v8/+/1846711
with a signed extract lane for I8x16 and I16x8.

Change-Id: I5a701417b772d12f5ef038efbb081716bb27e25a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1873700
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65307}