- Convert Builtin to enum class
- Change int-based builtin_index methods to use Builtin
- Change Builtins::builtin to Builtins::code

Change-Id: Id9e3bb83da97e8894ca7ca78e1e852da60675619
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2949104
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75127}