Update: Allow role=slider on button and input type=button elements

[scottaohara]

Upon reviewing implementations for sliders which use a <button> element as its base, I have not been able to come up with any present-day reasoning as to why role=slider would not be allowed on a button. At least, not any reasoning that could not also be problematic under other testable situations / WCAG rules. E.g., if the button is given a preventDefault(), then the implicit functionality which would make this a problematic role allowance can be avoided - and that functional issue could be found via other manual checks.

proposed resolution: allow role=slider on the button element and input type=button|submit|reset|image.