title: How to add icon inside textfield
body: <p>I have added icon to textfield using <code>icon: Icon(Icons.mail),</code> however it appears outside the textfield.</p>
  
  <p>How can the position of icon be changed so that it is displayed inside the textfield.</p>
  
  <p>TextField:</p>
  
  <pre><code>TextField(
    decoration: InputDecoration(
      icon: Icon(Icons.mail),
    ),
  ),
  </code></pre>