title: SVG Image as icon for AppBarToggleButton should look disabled
body: <p>I have a <code>AppBarToggleButton</code>, which has an <code>Image</code> set as content (the icon of the button). The source of the image is a SVG-file. When the button gets disabled, unfortunately, the icon stays black. Is it possible to gray out the icon too?</p>
  <p><a href="https://i.stack.imgur.com/RGdtH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RGdtH.png" alt="text is grayed out, the icon not" /></a>
  <a href="https://i.stack.imgur.com/gEk8z.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gEk8z.png" alt="enter image description here" /></a>
  (text is grayed out, the icon not)</p>
  <pre><code>&lt;AppBarToggleButton x:Name=&quot;spellCheckingToggleButton&quot; Label=&quot;Rechtschreibprüfung&quot;&gt;
    &lt;AppBarToggleButton.Content&gt;
      &lt;Image Source=&quot;/Assets/SpellChecking2.svg&quot;&gt;&lt;/Image&gt;
    &lt;/AppBarToggleButton.Content&gt;
  &lt;/AppBarToggleButton&gt;
  </code></pre>