This reverts commit f8a67670.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/25576

I don't think I've seen MSAN being flaky. Chances are that the change to SFI's object layout indeed left some field uninitialized.

Original change's description:
> Remove builtin-function-id in SFI
> 
> 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}

TBR=ulan@chromium.org,jgruber@chromium.org,leszeks@chromium.org,bmeurer@chromium.org,duongn@microsoft.com

Change-Id: Ic3964ce182ddbd7ef529ddb8b78b9bdfb1be7887
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6993
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1499500Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60018}