title: Required single selection on MaterialButtonToggleGroup
body: <p>Is there an option to make the <code>MaterialButtonToggleGroup</code> have a required selected button when using <code>app:singleSelection="true"</code>? </p>
  
  <p>When clicking to a different button works fine (all other buttons are deselected), but when you click the same (already selected) button it deselects it itself and I want to remain selected.</p>
  
  <p>My example:</p>
  
  <pre><code> &lt;com.google.android.material.button.MaterialButtonToggleGroup
        android:layout_width="wrap"
        android:layout_height="wrap_content"
        app:singleSelection="true"&gt;
  
        &lt;com.google.android.material.button.MaterialButton
          android:id="@+id/filterA"
          style="@style/Widget.MaterialComponents.Button.OutlinedButton"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="A"/&gt;
  
        &lt;com.google.android.material.button.MaterialButton
          android:id="@+id/filterB"
          style="@style/Widget.MaterialComponents.Button.OutlinedButton"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="B"/&gt;
  
        &lt;com.google.android.material.button.MaterialButton
          android:id="@+id/filterC"
          style="@style/Widget.MaterialComponents.Button.OutlinedButton"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="C"/&gt;
  
      &lt;/com.google.android.material.button.MaterialButtonToggleGroup&gt;
  </code></pre>