We introduce a new information type ForwardingIndex to be stored in
the Name::Hash field (to be used in the future).
To do so we use the 2 least significant bit to distinguish types
of information stored in the hash field (in contrast to only bit 1
to distinguis integer indicies from "real" hashes).
This motivated a refactor to use base::BitField for the hash field.

Bug: v8:12007
Change-Id: I651c86807edfc218792d0db12379374eaa50c930
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3432385Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78975}