Add a map in {IsolateInfo} to share export wrappers across modules. Each
entry is a weak handle which uses the finalizer to remove itself from
the map after the last strong reference dies.

R=clemensb@chromium.org

Bug: chromium:862123
Change-Id: I1f3a6af6aa4c4e42abfe587354ca14f9da916d91
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2448465Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70348}