Fix BeforeOptions search input missing aria-expanded

[alex-ju]

Summary

The search input in BeforeOptions has a role="combobox" which requires an "aria-expanded" attribute (set to "true" or "false") depending on the state.

Generally, the BeforeOptions is only visible when the PowerSelect is expanded, but since we have access to its state we can use @select.isOpen to conditionally apply this value.

Example

The example below uses the helpers-testing-single-power-select instance in the test-app with either a @labelText="Label" or an @ariaLabel="Label" provided to the <PowerSelect>.

Automated accessibility checks using axe

Before	After

Motivation

At @hashicorp we use <PowerSelect> extensively and we are grateful to see the many improvements introduced lately.

This change is primarily motivated by the desire to further improve the accessibility compliance of this component – in this instance, by providing the required aria attribute for the combobox element.

[mkszepp]

Thank you so much!