Is your feature request related to a problem? Please describe.

Previous discussions:

• Assigning role to Lightbox component #349
• VoiceOver announces offscreen slides #297

Describe the solution you'd like

Implement ARIA attributes according to WAI ARIA recommendations:

• https://www.w3.org/WAI/ARIA/apg/patterns/carousel/
• https://www.w3.org/WAI/ARIA/apg/patterns/carousel/examples/carousel-1-prev-next/

1. Set the following attributes on the portal node:

• role="dialog"
• aria-modal="true"
• aria-live="polite" ¹
• aria-roledescription="lightbox"

2. Set the following attributes on the root node in inline (carousel) mode:

• role="region"
• aria-live="polite" ¹
• aria-roledescription="carousel"

3. Set the following attributes on individual slides:

• role="region" ²
• aria-roledescription="slide"

¹ Will probably need to switch aria-live to "off" when Slideshow plugin starts playing slides, but postponing for now.

² Using region role on individual slides instead of group because otherwise VoiceOver stops announcing slide title and description.

Describe alternatives you've considered

No response

Additional context

No response