title: Use EventSystem for key-pressing events
body: <p>Context: say you're checking whether "W" is pressed on the keyboard, the most common way to check this is through the following code:</p>
  
  <pre><code>void Update(){
      if (Input.GetKeyDown("W"))
          DoSomething();
  }
  </code></pre>
  
  <p>Is there a way to do the following, using Unity's EventSystem? In other words, is there an implementation of an interface like <em>IPointerClickHandler</em>, for example, to check whether a button is pressed, without doing so in an <em>Update()</em> function?</p>