... capable of computing the forwarding pointer for objects allocated
outside of the main pointer compression cage.

Drive-by: hoist computation of pointer compression cage base out of
certain loops in GC code.

Bug: v8:11880
Change-Id: I23efdffd1a237d9eedd0e2975e8e40811417ef31
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3204968Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77244}