Back references to C++ objects may point to objects that never have
their graph nodes materializes through other C++ edges. We can just
create a graph node in this case, and avoid delaying the merging
completetly.

Bug: chromium:1244522
Change-Id: I0e9cb7a89ee90bfba217bc8475ac40bd7fe92a0b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3129426Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76583}