title: How to merge two lists and remove duplicates
body: <p>Given I have two list like the following:</p>
  
  <pre><code>var listA = new List&lt;string&gt; { "test1", "test2", "test3" };
  var listB = new List&lt;string&gt; { "test2", "test3", "test4" };
  </code></pre>
  
  <p>I want a third list with:</p>
  
  <pre><code>var listC = new List&lt;string&gt; { "test1", "test2", "test3", "test4"}
  </code></pre>
  
  <p>Is there a way to get this?</p>