Is there an existing issue for this?

• I have searched the existing issues
• I have read the guide to filing a bug

Use case

Hey,
I really like the new SearchBar / SearchAnchor.bar Widget!
However I think most of the suggestions will come from an async api call based on the input instead of prepared datasets.

Proposal

Something like this would be really nice:

SearchAnchor.bar(
  suggestionsBuilder: (context, controller) async {
    final suggestionList = await getSuggestions(controller.text);
    return suggestionList.map((suggestion) => 
      ListTile(
        title: Text(suggestion),
        onTap: () {
          //Some action
        },
      )
    );
  })