title: AvalonDock focus LayoutDocument content
body: <p>When a <code>LayoutDocument</code> is created and shown on screen, it gets the focus. I want to be able to put the focus on my content inside this document.</p>
  
  <p>How can I set the focus of my content inside the document after the document is shown?</p>
  
  <p>I have tried a few things like <code>ILayoutUpdateStrategy.AfterInsertDocument</code>, but the document isn't on the screen at this time. I can't find a hook that happens after the document is actually shown on screen.</p>