title: DateTimeFormat in TypeScript
body: <p>I want to display a time string in 24 hour format and thought it would be easy in TypeScript. But I can't use the Date.toLocaleTimeString() with options for some reason. Any idea why? They are defined in a separate interface definition.</p>
  
  <pre><code>interface Date {
      toLocaleString(locales?: string[], options?: Intl.DateTimeFormatOptions): string;
      toLocaleString(locale?: string, options?: Intl.DateTimeFormatOptions): string;
  }
  </code></pre>
  
  <p>The other option is to use Intl.DateTimeFormat but the constructors return a Collator? </p>
  
  <pre><code>var DateTimeFormat: {
      new (locales?: string[], options?: DateTimeFormatOptions): Collator;
      new (locale?: string, options?: DateTimeFormatOptions): Collator;
      (locales?: string[], options?: DateTimeFormatOptions): Collator;
  </code></pre>
  
  <p>Is it a copy paste bug in lib.d.ts (same for NumberFormat) or how am I supposed to use them?</p>
  
  <p>Hopefully it's an easy fix, I'm pretty new to TypeScript so I might have missed something.</p>