This uses the old trick from TypedArrays: a Smi-like all zero
pattern plus an offset that actually contains a raw address to access
off-heap data.

Bug: v8:7793
Change-Id: Ia44448d4ff7e2dcaa02a2c5653f622fb93c3dd09
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2534817Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71287}