title: mat-select-search is not a known element
body: <p>I am using this <a href="https://stackblitz.com/edit/mat-select-search?file=app%2Fapp.component.html" rel="nofollow noreferrer">stackblitz</a> to create mat-select. I copied the whole code including the mat-select folder and module. The whole code compiles perfectly without any error or issues. However, during page rendering time the code breaks and I get error <code>Unexpected directive 'MatSelectSearchComponent' imported by the module 'AngularMaterialModule'. Please add a @NgModule annotation.</code> 
  In the main HTML page where I am trying to use the mat-select there on mat-select-search tag, I am getting an error that <code>mat-select-search is not a known element</code>.
  Although the code compiles without any error. </p>
  
  <p>I tried importing mat-select-searchmodule in layout.component.ts then I am getting the below error</p>
  
  <pre><code> Type MatSelectSearchComponent is part of the declarations of 2 modules: MatSelectSearchModule and InsertModule! Please consider moving MatSelectSearchComponent to a higher module that imports MatSelectSearchModule and InsertModule.
  </code></pre>