Compaction currently considers only backing store pointers as slots and
those are uncompressed. The CL fixes the tests to use raw pointers
instead of Members.

Bug: chromium:1325007
Change-Id: I2ddfffeeab396552bb7cf31b2bd8502ebc2921fb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695590
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81056}