Although AccessorInfos are technically mutable, in practice they are not
mutated after initialization, and they are guaranteed to be immortal and
immovable. So, we can safely make them accessible from the off-thread
factory, as long as the user promises to not try to mutate them. This is
necessary for off-thread class boilerplate creation.

Bug: v8:10218
Bug: chromium:1011762
Change-Id: Id3108a2324a000ea0616b472dd77aed65b1f908e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2080351
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66563}