Add a framework for collecting event-based metrics like UKMs in V8
that is independent of the actual implementation.

Design doc: https://docs.google.com/document/d/1vCZQCh4B05isqwJOwTPv7WqcnVp4KJITMgsHSBg35ZI/

R=ulan@chromium.org

Bug: chromium:1101749
Change-Id: If3a5b954d1f0bcee4e06a03467b651feae378a5f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2288231
Commit-Queue: Emanuel Ziegler <ecmziegler@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69098}