This moves the existing PGO code to a separate cc file with a separate
header. As the implementation will be further extended in follow-up CLs,
it's better to have it separated.

R=jkummerow@chromium.org

Bug: v8:13209
Change-Id: I7b7b5bf9c8d3d542dae734f3874499dccee152a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3899321Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83250}