[iOS] Improve FRE Logging.

This CL updates the First Run Stage histogram for improved FRE analysis.

Change-Id: I837a560e435d08f54a8e04e819b0cd0430222991
Bug: 384917814
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6020088
Reviewed-by: Hira Mahmood <hiramahmood@google.com>
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Auto-Submit: Briana McClure <bmcclure@google.com>
Commit-Queue: Hira Mahmood <hiramahmood@google.com>
Cr-Commit-Position: refs/heads/main@{#1398805}