Rename AddSaturate and SubSaturate to the shorter version, AddSat and
SubSat, following the spec.

Bug: v8:10946,v8:10933
Change-Id: Idf74b3a1eb2e2f6d4e37d2b8e5fa6d96ea090db4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2436615Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70549}