title: Dart (Flutter) map<String, String>.map has no toList()
body: <p>I have a a map structure and I want to make a <code>DropdownMenuItem&lt;String&gt;</code> for each entry. What I try to do is to call <code>.map().toList()</code> like this</p>
  <pre><code>var _languages = {
    'en': 'English /',
    'fr': 'French ',
    'nl': 'Dutch',
    'es': 'Spanish'
  };
  
  languages.map((key, value) =&gt; DropdownMenuItem(
     value: key,
     child: Text(v)
  )).toList();
  </code></pre>
  <p>(if you are on a Windows, the US/GB is printed as text, if you are on any other platform, it will be flags). The problem now is twofold:</p>
  <ol>
  <li>The return type 'DropdownMenuItem' isn't a 'MapEntry', as required by the closure's context.</li>
  <li>The method 'toList' isn't defined for the type 'Map'.</li>
  </ol>
  <p>How would I properly create a list out of a map? Is this not possible because a map is not an ordered collection?</p>