MapRef::GetStrongValue now returns an Optional to account for the case
where we can't figure out the name of the bound function during
serialization. We could reach out to the heap in the future in this
case.

Fixed: chromium:1034203
Change-Id: I9fa81921b5dbd8bc9f68aa3c10921bc01b695a6b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1967386Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65470}