In certain scenarios, most notably Turbo navigation, <auto-complete> elements do not respond to events like keypresses and appear to be entirely non-functional. This is because the element relies on certain child elements being present in the DOM when connectedCallback fires, an assumption that is not always accurate, i.e. in the Turbo case. This PR adds a mutation observer that triggers a callback when the child elements have loaded. The callback performs the necessary setup that makes the element function normally.