Do not set aria-hidden on elements visible in the viewport

This is an amazing library. Kudos to the devs!

I noticed an accessibility issue in the slider.
The issue is that `aria-hidden` attribute is being set to `true` for elements which are in the slider view.
Please see this reproduction I made: https://codepen.io/geon-halfhelix/pen/YzeEbLj


Start with the linked CodePen reproduction and trace how the slider assigns aria-hidden to visible elements. The fix is done when elements currently in the viewport are not marked aria-hidden; verify the behavior against the reproduction and relevant accessibility checks.

Written by the indexing model from the issue text.