title: Typescript private class inside class or something similar
body: <p>I'd like to declare a private class, only to be used inside the file it was defined, is this possible?
  For example declared inside another class:</p>
  
  <pre><code>export class MyParentClass {
      class MyChildClass {
      }
  }
  </code></pre>
  
  <p>or inside the same file:</p>
  
  <pre><code>export class MyPublicClass {
     //Usage of MyPrivateClass 
  }
  
  class MyPrivateClass {
  }
  </code></pre>