Add client-side options support

# Problem
If there are static options passed into the element, the options are deleted on request for filtered options.

# Request
Client-side options should be supported and have filtering available. TBD: Do we allow both client-side (such as default options) *and* server-side options?

# Implementation concerns
## Accessibility
Ensure that any default / client-side options are announced when the input is focused. `screen-reader-announcements.ts` can assist with this.

When the options list isn't visible, an `aria-describedby` should be added to the input pointing to the feedback element. This should only be if the element has client-side options. Remove this `aria-describedby` when the user interacts with any key, and add it back in when the auto-complete-element is blurred. cc @github/accessibility and @jscholes for reference. "aria-live won't cut it" for this scenario

## Developer Notes
There is some initial setup done in `autocomplete.ts` to detect client-side options, but all of this can be removed / reworked, as long as accessibility considerations are met.

Commencez dans autocomplete.ts par examiner la détection existante des options côté client, puis lisez screen-reader-announcements.ts pour le comportement d’accessibilité. Suivez la manière dont les options sont supprimées pendant les requêtes filtrées et définissez l’interaction prise en charge entre les options côté client et côté serveur. Le travail est terminé lorsque les options côté client restent disponibles, que le filtrage fonctionne et que le comportement décrit concernant le focus, le clavier, le blur et aria-describedby est couvert.

Rédigé par le modèle d'indexation à partir du texte de l'issue.