cppgc: Rework prefinalizers

Move the check for whether an object is live or dead out of the
prefinalizer trampoline. Moving it into the backend allows for
inlining the check which avoids a call to the trampoline for live
objects.

On catapult benchmarks (e.g. cnn:2021, nytimes:2020), there's often
~2k finalizers registered. In order to avoid memory overhead in the
range of a few KB, we store the fact whether the object points to the
base object payload in the LSB of the pointer. For caged builds this
is replaced with just storing the index into the cage for both object
and base object payload.

Locally saves around ~10% of atomic sweeping processing time which is
in the order of .05ms.

Bug: v8:12698
Change-Id: I198205a6b1d57fc2df821ee4e73e53dc6f825ff5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3497764


Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79442}