[ads] SPIKE: Investigate possible causes for discrepancies between ad and advertiser-reported metrics

[tmancey]

Description

Investigate and resolve where needed:

• [ads] Clicks, conversions, and site visits do not work if a search result ad was opened in a new tab or window #40785
• What % is non-Brave browser usage?
• 5-second page landing timer differs from the advertiser's metric [page-lands do not work if the user opens the ad in a background tab; There is a bug with in-house ads where chrome://... does not match brave://...]
• 5-second timer is suspended if the user switches tabs and never returns to the tab, or restarts the browser
• JSON-LD validation [We should always call TriggerSearchResultAdEvent so that we can DumpWithoutCrashing within the ads component to investigate potential failures]
• [ads] Click metrics not recorded for New Tab Takeover and Brave News ads if the creative was removed from the catalog while the ad is visible #40899
• [ads] SPIKE: Investigate possibility of a race condition where a page navigation might complete before AdHandler::OnDidFire*AdClickedEvent is triggered #40898
• Check if confirmations could get stuck in the queue
• Verify that unit tests cover edge cases
• Simulate confirmation token redemption under different scenarios
• [ads] SPIKE: Investigate macOS notification ad click-through rates #41042
• Singleton tab
• Flagged/unflagged
• CR version
• Operating system version
• message_center::Notification
• GURL(kNotificationAdUrlPrefix + ad.placement_id)