broken by: [cleanup] Fix kPointerSize usages in src/objects/bigint.*

Bug: v8:8477, v8:8238
Change-Id: If1961ae42e1969d4ee807ea052a9c4cf4f072d0f
Reviewed-on: https://chromium-review.googlesource.com/c/1357046
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57997}