Only implemented and tested on arm64 and interpreter.

Moved a helper function (Clamp, renamed to Saturate) into src/utils to
be able to reuse this in interpreter and tests.

Bug: v8:10971
Change-Id: Iaffcd36d27e0e8ab11e167befa96eef8e59f1c81
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2438990Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70360}