title: Typescript conditional type based on writability
body: <p>Does typescript have a way to conditionally filter a type based on property writability or readability? For example:</p>
  
  <pre><code>interface Foo {
    readonly x: string;
    y: string
  }
  type FooOptions = Writable&lt;Foo&gt;; // { y: string }
  </code></pre>