and make the slot occupy two tagged words when pointer compression is enabled.

Tbr: bmeurer@chromium.org
Bug: v8:7703
Change-Id: Idcd3385cc7d5299d9bdaf6a69c7bd0591099f0bb
Reviewed-on: https://chromium-review.googlesource.com/c/1346489Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57693}