All strings in the internalized string list now have them.

Bug: v8:10506

Change-Id: I68feb34d0dc424465a53ac73a5d6b5297e29dd00
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218032
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68014}