This prototypes i32x4.widen_i8x16_s and i32x4.widen_i8x16_u for x64. It
uses some masks and pshufb for the widening.  These masks (3 for each
instruction) are stored as external references.

Bug: v8:11297
Change-Id: I6c8f55426bbb44b16ed552f393762c34c2524b55
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2617389
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72301}