feat: add "tabs" transform for `data-component` items
This feature is used in kroetenzaeune.de.
Example HTML widget:
<div data-component="tabs" class="tabs">
<ol class="tabbed-tabs">
<li><a href="#" class="tabbed-tab">foo</a></li>
<li><a href="#" class="tabbed-tab">bar</a></li>
<li><a href="#" class="tabbed-tab">baz</a></li>
</ol>
<ol class="tabbed-contents">
<li><div class="tabbed-content">foo-content</div></li>
<li><div class="tabbed-content">bar-content</div></li>
<li><div class="tabbed-content">baz-content</div></li>
</ol>
</div>
The widget is rendered in a tab representation and the first tab is selected (if one exists).