title: How to change icon when accordion summary is expanded?
body: <p>I want to change the icon based on whether the accordion is expanded or not.<br>
  <br>
  I see that on the material ui page that the CSS have .Mui-expanded which can see whether expanded={true} or false, but how can I use this to set a different icon when expanded is true or false.<br>
  <br>
  So I want to set IconA if expand is true and IconB if expand is false.<br></p>
  <pre><code>expandIcon={&lt;IconA/&gt;}
  </code></pre>