Add off-thread support for literals, including object/array boilerplates.
Notably, this includes adding FixedArray and HeapNumber support to
OffThreadFactory.

As a drive-by, OffThreadHandle is redefined to store an Address rather
than an Object, similar to Handle, so that it still works with forward
definitions of types.

Bug: chromium:1011762
Change-Id: I7c8452f450d8c57fe683a9e44532ce5647c84a11
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2036084
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66156}