title: SafeArgs not generating Directions / Args classes on a multi module project
body: <p>I created an empty project to try out the Navigation component. I wanted to see how it would behave with a multi module project (one common module with the majority of the dependencies, plus modules that would hold different parts of the app, and the <code>:app</code> module that would implement all of the modules).</p>
  
  <p>The top level gradle file has the dependency like so:</p>
  
  <pre><code>dependencies {
      classpath "com.android.tools.build:gradle:3.6.1"
      classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.61"
      classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.3.0-alpha04"
  }
  </code></pre>
  
  <p>The common module has these dependencies (among others):</p>
  
  <pre><code>dependencies {
      …
      api "androidx.navigation:navigation-fragment-ktx:2.2.1"
      api "androidx.navigation:navigation-ui-ktx:2.2.1"
      api "androidx.navigation:navigation-dynamic-features-fragment:2.3.0-alpha04"
      …
  }
  </code></pre>
  
  <p>And absolutely all the modules have this plugin applied on top:</p>
  
  <pre><code>apply plugin: "androidx.navigation.safeargs.kotlin"
  </code></pre>
  
  <p>Now, each "ui module" has fragments in it, and only the <code>:app</code> one implements a <code>main_graph.xml</code> that references to them. An example would be:</p>
  
  <pre><code>&lt;fragment
      android:id="@+id/registerFragment"
      android:name="example.register.RegisterFragment"
      android:label="RegisterFragment"&gt;
      &lt;action
          android:id="@+id/action_registerFragment_to_loginFragment"
          app:destination="@id/loginFragment" /&gt;
  &lt;/fragment&gt;
  </code></pre>
  
  <p>After all this is finished, a good Clean Project + Rebuild Project is done.</p>
  
  <p>To me, this makes sense. However, when I try calling the <em>theoretically</em> auto generated file <code>RegisterFragmentDirections</code> is not there, not in the specific sub module, not in the main one. The <code>NavDirections</code> can be found (so the dependencies somehow are working), but not the generated ones.</p>
  
  <p>I've tried implementing all the dependencies in each module, rolling back the navigation version to the previous alpha ones… no success.</p>