Some of the Array benchmarks were unintentionally spending a lot of
time on Number-to-String conversions. This patch avoids that, by
computing the dynamically-created strings only once.

Bug: chromium:1240981
Change-Id: If10826813d555398b45c22c958dee27e17f35d3c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3106747Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76387}