Using the external pointer table when compressing pointers lets us ease
the alignment requirement for the state field from 8-byte-aligned to
4-byte-aligned, as 8-byte alignment is not supported during compaction.

Bug: v8:12547
Change-Id: Ibbcb0d71f09f9bac66acc81459ab71e354ea405f
Cq-Include-Trybots: luci.v8.try:v8_linux64_pointer_compression_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3783077Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81979}