[A11Y] tablist needs tab roles for children elements

Description of the need

Backdrop tabs, such as those on /user have role="tablist" but the children tab links do not have role="tab". As per https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/ta..., the tab links need the tab role. It also states that the "panels" need have the role tabpanel, though given that only one is actually loaded to the page at a time, it's not clear if it makes sense.

Example from Mozilla:

<div class="tabs">
  <div role="tablist" aria-label="Sample Tabs">
    <button
      role="tab"
      aria-selected="true"
      aria-controls="panel-1"
      id="tab-1"
      tabindex="0">
      First Tab
    </button>
    <button
      role="tab"
      aria-selected="false"
      aria-controls="panel-2"
      id="tab-2"
      tabindex="-1">
      Second Tab
    </button>
    <button
      role="tab"
      aria-selected="false"
      aria-controls="panel-3"
      id="tab-3"
      tabindex="-1">
      Third Tab
    </button>
  </div>
  <div id="panel-1" role="tabpanel" tabindex="0" aria-labelledby="tab-1">
    <p>Content for the first panel</p>
  </div>
  <div id="panel-2" role="tabpanel" tabindex="0" aria-labelledby="tab-2" hidden>
    <p>Content for the second panel</p>
  </div>
  <div id="panel-3" role="tabpanel" tabindex="0" aria-labelledby="tab-3" hidden>
    <p>Content for the third panel</p>
  </div>
</div>