[Privacy Sandbox] Clear Ad API prefs on startup if feature enabled

Introduces `ClearAdPrivacyPrefs` method to set the Privacy Sandbox M1 Ad
API prefs (Topics, Site Suggested Ads, and Ad Measurement) to false.
This clearing logic is invoked during the profile pref migration in
browser_prefs.cc and is gated by the
`PrivacySandboxAdPrivacyUxDeprecation` feature.

Bug: 494265981
Change-Id: I8bf5b1e431aed528452548970991b1510d8e04b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7689451
Reviewed-by: Dominic Battre <battre@chromium.org>
Commit-Queue: Jacob Stanley <jacobstanley@google.com>
Reviewed-by: Abe Boujane <boujane@google.com>
Cr-Commit-Position: refs/heads/main@{#1603732}