For replacing lanes (i8x16 and i16x8) the replacement value is stored in
a word32. Simply storing it will cause us to have the wrong value, we
need to mask (for overflow) and extend appropriately.

Same for extracting, the values are stored in sign-extended form,
unsigned extracts should zero the top bits.

Bug: v8:10507
Change-Id: If5ed79f5b6bdb64f900a54b9e148b2d96a74f312
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2436612Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70210}