title: Issue with mat-icon module when used at inner level of folder structure
body: <p>I have imported mat icon module in the module and i am trying use mat-icon inside few component with the nested folder within. but It's giving the error.</p>
  
  <pre><code>Tried declaring at root level in app.module.
  
  'mat-icon' is not a known element:   
  1. If 'mat-icon' is an Angular component, then verify that it is part of this module.
  
  &lt;div class="upload-icon"&gt;[ERROR -&gt;] &lt;mat-icon aria-label="arrow upward icon"&gt;arrow_upward&lt;/mat-icon&gt;&lt;/div&gt;
  </code></pre>