clang now complains when a BitField for an enum is too wide.
We could suppress this, but it seems kind of useful from an
uninformed distance, so I made a few bitfields smaller instead.

(For AddressingMode, since its size is target-dependent, I added
an explicit underlying type to the enum instead, which suppresses
the diag on a per-enum basis.)

This is without any understanding of the code I'm touching.
Especially the change in v8-internal.h feels a bit risky to me.

Bug: chromium:1348574
Change-Id: I73395de593045036b72dadf4e3147b5f7e13c958
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3794708
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82109}