title: vscode.workspace.openTextDocument fails silently
body: <p>With the same value for Uri, <code>openTextDocument</code> fails to have any discernible effect yet <code>executeCommand</code> successfully opens the document.</p>
  
  <pre><code>vscode.workspace.openTextDocument(uri);
  vscode.commands.executeCommand("vscode.open", uri);
  </code></pre>
  
  <p>Are there any known problems with <code>vscode.workspace.openTextDocument</code>?</p>