WrapperDescriptor is used to describe how JS wrapper objects can be
inspected to find C++ wrappable objects. In addition, to specifying
which embedder fields are used to find type and instance, the
descriptor also provides and embedder id that identifies
garbage-collected objects. It is expected that the first field of the
type is a uint16_t with that id.

Bug: chromium:1056170
Change-Id: I9cf8d79db972f2dea023114fd5a567e89a3bf373
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2688399Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72657}