This adds HeapObjectHeader, a meta object that is put in front of
every managed object. HeapObjectHeader provides accessors for:
1. GCInfoIndex
2. In construction bit
3. size
4. Mark bit

Meta info is distributed among two uint16_t fields as (1.,2.) and
(3.,4.). This is convenient as the non-bit accessors (size,
GCInfoIndex) are constant during marking.

Object layout see heap-object-header.h.

Note: The current implementation does not bypass ASAN poisoning and
assumes an unpoisoned header whenever performing an access.

Bug: chromium:1056170
Change-Id: I753f15467ed5c2b22b47e64d3aa5a3c1baddf8e1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2116031
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66861}