Sync with
https://github.com/tc39/proposal-intl-segmenter/pull/55
and
https://github.com/tc39/test262/pull/1994

Bug: v8:8588
Change-Id: Ifc46779f156ea986e3dbe6a632a781bb7134112b
Reviewed-on: https://chromium-review.googlesource.com/c/1374997Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58301}