This patch adds tab-to-search results, partially reusing the existing code in `UrlbarProviderAutofill._matchSearchEngineDomain`. Tests are included. Telemetry is included in a child revision.

This patch doesn't add the "Search <engine name> directly from the address bar." action text. Our current action text code l10n is in a .properties file and I thought adding branching translation logic in UrlbarView would be a mess. I think Marco might be converting that .properties file to Fluent in bug 1658629. If he is, I'll rebase my patch on his and add the new action text it in this patch. If he isn't, I'll file a follow-up for converting that .properties file and adding the tab-to-search action text, which we can address before preffing `update2.tabToComplete` on. Either way, I think this is ready for a first-round review.

This patch is based on D91076 and D91077. It doesn't have any functional dependency, but there are some conflicts, especially in the added telemetry.

Differential Revision: https://phabricator.services.mozilla.com/D91468