title: traverse keys of enum gives typing issue
body: <p>Suppose you want to print all values of an enum</p>
  <pre><code>enum AnEnum {
      a = 'a',
      b = 'b'
  }
  
  const keys = Object.keys(AnEnum);
  
  keys.forEach(key =&gt; {  
       console.log(AnEnum[key]);
  });
  </code></pre>
  <p>This gives the following error</p>
  <blockquote>
  <p>Element implicitly has an 'any' type because expression of type
  'string' can't be used to index type 'typeof AnEnum'.   No index
  signature with a parameter of type 'string' was found on type 'typeof
  AnEnum'</p>
  </blockquote>
  <p><a href="https://i.stack.imgur.com/nPMD6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nPMD6.png" alt="enter image description here" /></a>
  <a href="https://www.typescriptlang.org/play?#code/KYOwrgtgBAgiCi5oG8BQUNQIZQLxQHIsCAadTAIz0IoNQF9VUBjAexAGcAXKAa2ACeHagHkKAK2DMuAOn5CAFHESQAlAG4m8jjIBmrAE7wszABYL5eAHxRkGcpjadWAG2AyXrAOZKESANryALoaDKFAA" rel="nofollow noreferrer">DEMO</a></p>
  <p>I was only able to fix this is with adding <code>any</code></p>
  <pre><code>(AnEnum as any)[key]
  </code></pre>
  <p>but I guess there should be better solution. Any suggestions?</p>