Document:
- TraceCallback
- TraceDescriptor
- TraceTrait

Bug: chromium:1056170
Change-Id: I1c57ce215e4f6f83563326924cfc4c6aeef33e41
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235112
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68225}