Design Doc: https://goo.gl/PGUQ1d

Use template to share code between formatRange and formatRangeToParts
Lazy crate DateIntervalFormat inside formatRange/formatRangeToParts to
reduce performance impact.

Bug: v8:7729
Change-Id: I130748a5ff7ca11235e6608195d365e58d440580
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1556573
Commit-Queue: Frank Tang <ftang@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60930}