title: Protobuf not generating correct imports when using java_multiple_files in intellij
body: <p>With <code>example.proto</code> below:</p>
  
  <pre><code>syntax = "proto3";
  package pack;
  
  option java_package = "pack";
  option java_multiple_files = true;
  
  message TestEvent {
      int32 id = 1;
  
  }
  </code></pre>
  
  <p>And generating it with Protoc, some classes are generated:</p>
  
  <ul>
  <li>Example.java</li>
  <li>TestEvent.java</li>
  <li>TestEventOrBuilder.java</li>
  </ul>
  
  <p>The problem is that the auto-generated TestEvent class doesn't compile.  It's class declaration is generated as</p>
  
  <pre class="lang-java prettyprint-override"><code>public final class TestEvent extends com.google.protobuf.GeneratedMessageV3 implements TestEventOrBuilder { 
      //... Auto-generated class
  }
  </code></pre>
  
  <p>But <code>TestEevent</code> doesn't import <code>TestEventOrBuilder</code>, that's the reason it doesn't compile (The problem is a simple <code>cannot resolve symbol TestEventOrBuilder</code>), accoring to Intellij. When trying to solve it's own way, <code>Intellij IDEA</code> changes the class to </p>
  
  <pre><code>public final class TestEvent extends com.google.protobuf.GeneratedMessageV3 implements pack.TestEventOrBuilder
  </code></pre>
  
  <p>Is this a known issue with <code>Protobuf</code> and Intellij? How to fix the auto-compilation to understand <code>TestEventOrBuilder</code>?</p>