Synthesize an extra AutocompleteSuggestion at the top of the Search
Suggestions section whenever there is a configured search engine and
the typed query is not URL-shaped.
Use the query as the row's primary text, carry a "Search with <engine>"
subtitle, and render that subtitle in the AppKit and Qt popups so the
explicit search fallback stays visible and readable even when history
fills the list.
Render AutocompleteSuggestion rows with section headers, favicons,
titles, and secondary text in the child-window popup instead of just
plain strings.
Move the AppKit popup and inline completion onto the shared suggestion
model, and share the base64 PNG decoding helper with the application
menu icon loading path.
Replace the AppKit popover because it becomes key and steals focus from
the location field while suggestions are visible. Use a borderless
child window anchored to the toolbar item instead, and dismiss it on
resize or focus changes so the browser chrome stays predictable.
The autocomplete popover on macOS was stealing focus from the location
bar when suggestions were displayed. This change saves the current
first responder before showing the popover and restores it immediately
after, ensuring the user can continue typing without interruption.
