Also add some simple unittests for these functions.

Bug: v8:10696
Change-Id: Ic7607780b4eaf275b20d0937bf214846bf51d539
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2330806Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69183}