1. Sync with
https://github.com/tc39/proposal-unified-intl-numberformat/pull/57
so the formatting of {style: "unit" unit: "percent"} and
the formatting of {style: "percent:"} are treated different that
simplified the algorithm.
2. Store style into bit flags because we need it quickly during format.
3. Add more unit tests and regression test.

Bug: v8:9498
Change-Id: I75ed22fef1feb73ebf624bda70ebe45b80e7bc8b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1704948Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62834}