This makes the API more consistent.

Originally I planned to use this to template iterators inside mkgrokdump, but
I decided against it.

Bug: v8:9183
Change-Id: Iefa372370a7cc7c637dc86c0bfb837a91a2bc6e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622116Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#61705}