For packaging shapes and materials, display autocomplete suggestions without having to type the first character

[stephanegigandet]

Reported by @thomas-algo in #3744

Packaging shapes and materials suggestions are listed by popularity, and the first suggestions cover a big percentage of the products, so it makes a lot of sense to display the suggestions without having to type the first character, especially if we pass the product category, and/or the shape as offered by openfoodfacts/openfoodfacts-dart#695

See also #3749

[stephanegigandet]

Note that at this time, suggestions are ordered by popularity only for packaging shapes and materials, so we should not do this for other taxonomies, as otherwise we would get suggestions in alphabetic order. For other suggestions, it makes sense to wait for at least 1 character.