issue #13556 Add aria role of option,aria-selected and tabindex based ke...

...yboard navigation
Refs #13556.
Neither do I, just wanted to throw this in, as [that's what we do](https://github.com/twbs/bootstrap/blob/ed8228e1cbf73c1919c291054f4ea1309923cdae/less/scaffolding.less#L121-L134) for our `.sr-only` class. Maybe @mdo can chime in here and recommend a solution?