This is the 2. CL in a series of CollectGarbage refactoring CLs.

It moves two kinds of callbacks to the epilogue of CollectGarbage:
- Weak second pass phantom callbacks
- GCEpilogueCallbacks

As the prologue callbacks have also been moved outside the GC cycle,
with this CL the need for nesting tracers is eliminated. DCHECKs are
put in place to ensure this.

Bug: v8:12503
Change-Id: I0bc2c0fa0de1b0ffc32b5c648a612c0b3e0e1f3e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3427199Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78883}