4 instructions, i8x16, i16x8, i32x4, i64x2 relaxed lane select. These
instructions only guarantee results when the entire lane is set or
unset, so vpblendvb will give correct results for all of them.

Same instruction selector code as x64.

Bug: v8:12284
Change-Id: Icd0bc8c5125cd2780141117830d6cb6e6babbb74
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3251701Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77779}