title: mat-select not working in mat-expansion-panel
body: <p>We have to show a form inside mat-expansion-panel. There are multiple fields in the form, for few of them I am using mat-select and for another few I am using mat-input.</p>
  
  <p>In expansion panel, matInput is working fine but mat-select is not showing the options for selecting a possible value.</p>
  
  <p>Though mat-select is working fine when showed normally.</p>
  
  <pre><code>   &lt;mat-expansion-panel&gt;
          &lt;mat-expansion-panel-header&gt;
              Heading 1
          &lt;/mat-expansion-panel-header&gt;
          &lt;mat-form-field&gt;
              &lt;mat-select placeholder="Select"&gt;
                  &lt;mat-option value="1"&gt;option 1&lt;/mat-option&gt;
                  &lt;mat-option value="2"&gt;option 2&lt;/mat-option&gt;
                  &lt;mat-option value="3"&gt;option 3&lt;/mat-option&gt;
                  &lt;mat-option value="4"&gt;option 4&lt;/mat-option&gt;
              &lt;/mat-select&gt;
          &lt;/mat-form-field&gt;
      &lt;/mat-expansion-panel&gt;
  </code></pre>
  
  <p>Any help is appreciated.</p>