builtin_function_id corresponded to BuiltinFunctionId (a manually maintained list of 'interesting' functionsmainly used during optimization). With this change, we nuke builtin-function-id in favor of builtin-id and 8 bits is freed up in SFI.

Bug: v8:6993
Change-Id: Iee9b539475bc6531c9aa65b1904d1402a9ef30db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1495898
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60017}