- Use kNoBuiltinId instead of literal -1.
- Remove support for non-embedded builtins.
- Update Code object layout comment.

Bug: v8:10933
Change-Id: Ie75c6ccc0a0f19348ae214249a8fc81f7e91df0c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2474115
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70557}