Reflect recent change to the proposal

http://tc39.es/proposal-intl-DateTimeFormat-formatRange/#sec-intl.datetimeformat.prototype.formatRange

Bug: v8:10681
Change-Id: Ie2e0e85816aeaeb2615d482ccd3ea345a5056c93
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2286813
Commit-Queue: Frank Tang <ftang@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68748}