Registers were supposed to fit in an int, but some register subclasses
added extra fields which made them too big. This fiddles around with
field sizes so that all the Register subclasses still fit inside of an
int (by making the Register code field 8-bit etc).

Change-Id: I31ffbc8f98b6a5e1f638fc59147009e5f81dff41
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3513612
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79421}