title: Bootstrap 4 form input with icon for validation
body: <p>In Bootstrap 3 there were optional icons for each of the validation states. The icon would appear in the right side of the input using the <code>has-feedback</code>, <code>has-success</code>, <code>has-danger</code>, etc... classes.</p>
  
  <p><a href="https://i.stack.imgur.com/ZHi1G.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ZHi1G.png" alt="enter image description here"></a> 
  How can I get this same functionality in Bootstrap 4 using the <code>valid-feedback</code> or <code>invalid-feedback</code> classes?</p>