When walking the stack and visiting compressed spill slots, maintain
their compressedness so that generated code can rely on spilled values
not magically changing.
Tested manually using the benchmark in the associated bug, as I'm not
sure how to create a fast, reliable regression test for this.

Fixed: v8:13216
Change-Id: Iebd1fb513975d9ee2567f7141f3ab18a04b0f4e1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3854507
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82705}