title: RouteComponentProps from react-router-dom with custom properties
body: <p>I have a component called Navbar which uses the location object from history, as defined in RouteComponentProps.</p>
  <p>I tried to add a custom prop to my component like so:</p>
  <pre class="lang-js prettyprint-override"><code>interface IProps{
     title?: string
  }
  
  class Navbar extends React.Component&lt;RouteComponentProps&lt;{}&gt; &amp; IProps&gt;{
  
  }
  </code></pre>
  <p>While this does not throw an error, when I try to do:</p>
  <pre><code>&lt;Navbar title=&quot;My Custom Page Title&quot; /&gt;
  </code></pre>
  <p>Typescript complains with:</p>
  <p>Type '{ title: string; }' is not assignable to type '(IntrinsicAttributes &amp; IntrinsicClassAttributes&lt;Component&lt;Pick&lt;RouteComponentProps&lt;any, StaticContext, unknown&gt;, never&gt; | (Pick&lt;RouteComponentProps&lt;any, StaticContext, unknown&gt;, never&gt; &amp; { ...; }), any, any&gt;&gt; &amp; Readonly&lt;...&gt; &amp; Readonly&lt;...&gt;) | (IntrinsicAttributes &amp; ... 2 more ... &amp; Readonly&lt;...&gt;)'.
  Property 'title' does not exist on type '(IntrinsicAttributes &amp; IntrinsicClassAttributes&lt;Component&lt;Pick&lt;RouteComponentProps&lt;any, StaticContext, unknown&gt;, never&gt; | (Pick&lt;RouteComponentProps&lt;any, StaticContext, unknown&gt;, never&gt; &amp; { ...; }), any, any&gt;&gt; &amp; Readonly&lt;...&gt; &amp; Readonly&lt;...&gt;) | (IntrinsicAttributes &amp; ... 2 more ... &amp; Readonly&lt;...&gt;)'.ts(2322)</p>
  <p>Originally, I had tried this:</p>
  <pre><code>interface IProps extends RouteComponentProps{
     title?: string
  }
  </code></pre>
  <p>But I also get a typescript error.</p>
  <p>I am not sure what the correct method is for extending or expanding RouteComponentProps.</p>