title: Access FastImage once it is fetched from url and convert to base64 in react native
body: <p>I have standard fastimage code:</p>
  <pre><code>&lt;FastImage
      source={{
          uri: imageUrl,
          priority: FastImage.priority.normal,
      }}
  /&gt;
  </code></pre>
  <p>The issue I am having is that I need to convert this image to base64.  I cannot figure how to access the image file once it is fetched from the server without fetching from the server a second time, which I don't want to do.</p>