The heap snapshot view in the dev tools reports some incorrect retaining
paths involving weak references from relocation data in Code objects.
This change updates IndexedReferencesExtractor::VisitEmbeddedPointer to
better match the behavior in MarkingVisitorBase.

Drive-by cleanup: ObjectVisitor::VisitRelocInfo needn't be virtual
because there's only one implementation.

Bug: v8:12126
Change-Id: I669a7408e7a46e797b8c2b372235b4ea42ee22e1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3107214Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#76406}