Resolve a TODO to remove cached template objects from the template cache
which have a cleared weak pointer to the template object. Requires a
little bit of awkward code to handle the "head is dead" case, but OTOH
the implementation cleans up the second Lookup of the head.

Bug: v8:13190
Change-Id: I31a8d8ab77e04c8496a2cacb6154f2ee84d6a795
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3899257
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83249}