fix(core): segmented button accessibility improvements

[mikerodonnell89]

fixes #10805

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[InnaAtanasova]

<ul 
    role="listbox" 
    aria-multiselectable="false" 
    aria-orientation="horizontal"
    aria-roledescription="Segmented button group" 
    aria-describedby="..." 
    class="..." 
    tabindex="-1">
    <li 
      tabindex="-1" 
      role="option"
      aria-roledescription="Segmented button" 
      aria-posinset="1" 
      aria-setsize="3" 
      aria-selected="false"
      class="..." 
      style="...">
    ...
    </li>
    <li 
      tabindex="0" 
      role="option"
      aria-roledescription="Segmented button" 
      aria-posinset="2" 
      aria-setsize="3" 
      aria-selected="true"
      class="..." 
      style="...">
      ...
    </li>
    <li 
      tabindex="-1" 
      role="option"
      aria-roledescription="Segmented button" 
      aria-posinset="3" 
      aria-setsize="3" 
      aria-selected="false"
      class="..." 
      style="...">
      ...
    </li>
  </ul>

[InnaAtanasova]

https://www.w3.org/WAI/ARIA/apg/patterns/listbox/