This in in preparation for generic (off-heap/on-heap) bytecode
array accessor.

Bug: v8:7790
Change-Id: Ib419831ba1db95ab938179723ef5f130f01ae0d6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1635895
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62222}