Autocomplete

A text field with suggestions, where the filtering is yours and the semantics are not.

Bits owns `aria-activedescendant`, arrow navigation, the field keeping focus
while the highlight moves in the list, and the list closing correctly. That
combination is why a hand-written autocomplete is almost always unusable with
a screen reader.

The filtering is yours: `onsearch` fires and you decide what `items` becomes.
That means the same component works over a local array and over a query to the
server, and the component never has to guess which.