Tabs accessibility: missing aria roles & attributes

[ygatesoupe]

Tab heading <a class="nav-link"> is missing role="tab", aria-expanded and aria-controls

Tab content misses the aria-expanded attribute but yet has role="tabpanel" and aria-labelledby (which is great).

<ngb-tabset>
    <ul role="tablist" class="nav nav-tabs">
      <li class="nav-item">
        <a class="nav-link active" href="" id="ngb-tab-0">
          Simple
        </a>
      </li>
    </ul>
    <div class="tab-content">
        <div class="tab-pane active" role="tabpanel" aria-labelledby="ngb-tab-0">
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        </div>
    </div>
  </ngb-tabset>

Bootstrap implementation

[pkozlowski-opensource]

Thnx for brining this up. Would you mind sending us a PR with updates to the tabset component? Thnx!