[ads] Sanity test iOS `NotifyTab[Html/Text]ContentDidChange` business logic

[tmancey]

Sanity test:

• [x] Confirm that we do NOT call ads_service_->NotifyTabHtmlContentDidChange or ads_service_->NotifyTabTextContentDidChange if restoring a tab
• [ ] Confirm that we do NOT call ads_service_->NotifyTabHtmlContentDidChange or ads_service_->NotifyTabTextContentDidChange if the tab is NOT a new navigation (user tapped forward/back button or refreshed the tab)
• [ ] Confirm that we do NOT call ads_service_->NotifyTabHtmlContentDidChange or ads_service_->NotifyTabTextContentDidChange if the tab redirect chain is empty
• [ ] Confirm that we do NOT call ads_service_->NotifyTabHtmlContentDidChange or ads_service_->NotifyTabTextContentDidChange if the tab is displaying an error page
• [ ] Confirm that we do NOT call ads_service_->NotifyTabTextContentDidChange for non-Rewards users
• [ ] Confirm that we call ads_service_->NotifyTabHtmlContentDidChange and ads_service_->NotifyTabTextContentDidChange if the tab web content is a single page application (same document)
• [ ] Confirm that we call ads_service_->NotifyTabHtmlContentDidChange and ads_service_->NotifyTabTextContentDidChange if the tab web content is a multi page application (document changed)

Please fix any bugs via this issue because they would affect conversions, purchase intent and text classification. See desktop/Android business logic in brave/browser/brave_ads/tabs/ads_tab_helper.cc