title: Issue when mat-sidenav-container and mat-sidenav in different components
body: <p>I have separated out mat-sidenav-container and mat-sidenav into two different components. When I have my sidenav in two components like this, the mode "side" is not working anymore. The mode switch to "over".
  When I have all in the same component, it's working.</p>
  
  <pre><code>&lt;app-layout&gt;
   &lt;app-sidenav&gt;&lt;/app-sidenav&gt;
   &lt;router-outlet&gt;&lt;/router-outlet&gt;
  &lt;/app-layout&gt;
  </code></pre>
  
  <p><strong>app-layout</strong> contains <strong>mat-sidenav-container</strong> component and
  <strong>app-sidenav</strong> contains <strong>mat-sidenav</strong> component</p>
  
  <p>During runtime,</p>
  
  <pre><code>&lt;app-sidenav&gt;&lt;/app-sidenav&gt;
  &lt;router-outlet&gt;&lt;/router-outlet&gt;
  </code></pre>
  
  <p>gets wrapped by mat-sidenav-content.</p>