No changes to the algorithm; minor speedup due to the move
from Handle<BigInt> to Digits.

Bug: v8:11515
Change-Id: Id85fe4f0c276d3ad826fee79205719092d0e0715
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2947412
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75158}