[Accessibility Docs] Slider

Using [this template](https://docs.google.com/document/d/1IwFMfJrTfJPXDcVJfLWXYkw-pjgWhBWo4GX8X098Q64/edit#), create accessibility docs for [Slider](https://vanillframework.io/docs/patterns/slider)

Start with the linked accessibility documentation template and the Slider pattern page. Create accessibility documentation for Slider using that template; the work is done when the requested Slider docs are complete and aligned with the template.

Written by the indexing model from the issue text.