title: UWP - bind element to main window size AND also update the value as window size changes
body: <p>I want to bind to a text block the current size of the window.
  In the current implementation the size of the main window is set at run time BUT if I resize the window after the application has launched the new size is not updated in the text block.</p>
  
  <pre><code>&lt;Grid x:Name="grid" Background="#FFE8E8E8"&gt;
     &lt;TextBox x:Name="textBoxSample" Width="300" Height="200" Text="{Binding ActualWidth, ElementName=grid}"&gt;&lt;/TextBox&gt;
  &lt;/Grid&gt;
  </code></pre>