This just moves the existing algorithm, and translates it from
Handle<BigInt> to Digits as underlying data format.

Bug: v8:11515
Change-Id: Ieefee4e953e14f4c574aebab94d825ddb7c31f8c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2975304
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75391}