Before adding serialization of tiering information, refactor the
existing code to use a {ProfileGenerator} class. This makes it easier to
add new methods that can use all existing fields (instead of having new
functions that need a lot of parameters).

R=jkummerow@chromium.org

Bug: v8:13209
Change-Id: I0946cb1d507fde9e6d680ad588ba963c539d1d0c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3899301
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83257}