Since next() comes from ThreadedListTraits, the users of this class
can modify the list by modifying the next pointer. This however breaks
the invariant that `tail_` points to the last element of the list.

We ensure this invariant lazily. This should be _almost_ no effect
for users that do not manually modify the next pointer.

Change-Id: If46283ab4fc5036a81f353b25823b0fd39b3e232
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3578803Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80042}