[Intl] Use icu::LocaleBuilder for JSLocale

Performance impact measured by
$ python -u tools/run_perf.py --binary-override-path \
    out/x64.release/d8 --filter "JSTests/Intl"  \
    test/js-perf-test/JSTests5.json

Look for NewIntlLocaleWithOptions-Intl & NewIntlLocale-Intl (3 runs):
BEFORE . 465 / 473 / 438                 1717 / 1677 / 1719
AFTER    553 / 520 / 463                 2706 / 2530 / 2758
Speed up      x1.12                            x1.56

Bug: v8:9121

Change-Id: I0f88a712203639972c0c90fcfc0a89f01da90d73
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1570581Reviewed-by: Frank Tang <ftang@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61560}