use ARIA Roles and Attributes around JS viewers to work on better default accessibility for non custom theme implementers

[DiegoPino]

What?

Example is https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Reference/Roles/img_role
Can be used around (formatter level) of Mirador/OSD, etc

some ways like <img alt="some alt"> are great but IIIF driven display is mostly via viewers so we need to have compatible/modern A11y ways in place that the user can setup too via the UI/settings without custom work or Theme work

@alliomeria https://developer.mozilla.org/en-US/docs/Web/Accessibility