title: How do "theme" icons work in Qt Creator Designer?
body: <p>When I create the "Command link button" (<code>QCommandLinkButton</code>) it has relatively nice green arrow icon. </p>
  
  <p><img src="https://i.stack.imgur.com/2UA9c.png" alt="image description"></p>
  
  <p>I would like to see what other nice icons can I choose. When I try to change the icon, <code>[Theme]</code> appears instead of path or some GUI selection dialog:</p>
  
  <p><img src="https://i.stack.imgur.com/QE36L.png" alt="image description"></p>
  
  <p>I also noticed the context menu:</p>
  
  <p><img src="https://i.stack.imgur.com/rh0X6.png" alt="image description"></p>
  
  <p>When I click <em>Set icon from theme</em>, again expecting some GUI selection list, I get just a text field:</p>
  
  <p><img src="https://i.stack.imgur.com/Krg2y.png" alt="image description"></p>
  
  <p>What I was imagining:</p>
  
  <p><img src="https://i.stack.imgur.com/sCW9y.png" alt="image description"></p>
  
  <p>Where's the list of icons from which the green arrow was taken?</p>