[combobox] accessibility in documentation

[GarthDB]

Description

Combobox is not currently using the correct DOM for Aria.

React Spectrum might have worked toward fixing this in their code base.

[castastrophe]

PickerButton seems to be using the right arias in our Storybook though we haven't mapped all the appropriate events (just click) so that the interaction isn't reflecting a production implementation.

Can we update the goal of this issue to cover adding expected events to the demo as well?

https://opensource.adobe.com/spectrum-css/?path=/story/components-combobox--default