Code objects for builtins are immortal and immovable and can thus be
dereferenced like read-only-objects.

Bug: v8:10315
Change-Id: I60d961fee71056160ad2913bffe3ca50280cb9d2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2465835Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70471}