Provide a more complete BigInt API.

Bug: v8:7712
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Ic8562d616f3125deabdf8b52c7019b191bef0e07
Reviewed-on: https://chromium-review.googlesource.com/1101198
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54122}