title: Animating UIButton configuration change
body: <p>Modern <code>UIButton</code> <a href="https://developer.apple.com/documentation/uikit/uibutton/3784627-configuration" rel="nofollow noreferrer">configuration API</a> allows for new way of setting button appearance. However the code below skips the animation entirely.</p>
  <pre><code>@IBAction func buttonTouched(_ sender: UIButton) {
      sender.configuration?.background.backgroundColor = .green
      UIView.animate(withDuration: 0.4, delay: 0.5) {
          sender.configuration?.background.backgroundColor = .systemMint
      }  
  }
  </code></pre>
  <p>Similar thing can be done like this:</p>
  <pre><code>@IBAction func buttonTouched(_ sender: UIButton) {
      sender.backgroundColor = .red
      UIView.animate(withDuration: 0.4, delay: 0.5) {
          sender.backgroundColor = .systemMint
      }
  }
  </code></pre>
  <p>And this works. The question is how to animate <code>UIButton</code>'s configuration changes.</p>