This refactors the constant pool handling for arm64. The immediate goal
is to allow 32bit compressed pointers in the pool. The mediate goal is
to unify the implementation with the arm constant pool, which will be
done in a follow-up CL.

Bug: v8:8054
Change-Id: I74db4245e5e1025f2e4de4144090fa4ce25883ab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1645316Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62209}