title: What is a purpose to provide a key when creating public widgets?
body: <p>In <code>flutter_lints</code> the <code>use_key_in_widget_constructors</code> lint requres providing a key when creating public widgets.</p>
  <blockquote>
  <p>It's a good practice to expose the ability to provide a key when
  creating public widgets.</p>
  </blockquote>
  <pre><code>class MyPublicWidget extends StatelessWidget {
    MyPublicWidget({Key? key}) : super(key: key);
  }
  </code></pre>
  <p>What is actualy the purpose of this lint rule i.e. what it gives?</p>