as part of the ongoing quest to get rid of Object*/Object** entirely.
Turns out the Deserializer was actually using unaligned MaybeObject**
pointers, which is undefined behavior. This patch makes the unaligned
values obvious (as "UnalignedSlot") and safe.

Bug: v8:3770
Change-Id: I20f2cca10cc025fa4867e56d9d740a3653837749
Reviewed-on: https://chromium-review.googlesource.com/c/1295792
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56924}