1. Add Intl::NumberFieldToType to support RelativeTimeFormat
by refactoring IcuNumberFieldIdToNumberType
2. Use formatNumericToValue / formatToValue to implement formatToParts

Bug: v8:8837
Change-Id: I4d8fab9c337ec02eeb3500b4c0f90547e48444e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1560661Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60797}