title: Navigation Architecture Component: transition animations not working for dialog
body: <p>I have a <code>&lt;dialog</code> in my nav graph with enter/exit anims but the animations aren't working for the dialog.  I've tested them on <code>&lt;fragment</code> nodes and those work fine. </p>
  
  <p>For clarification, the dialog being referenced is a DialogFragment</p>
  
  <p>Is this a limitation or am I doing something wrong?</p>
  
  <p>Here's the relevant snippet from my nav graph:</p>
  
  <pre><code>&lt;fragment
          android:id="@+id/fragment_home"
          android:name="com.my.project.fragments.HomeFragment"
          android:label="@string/nav_home"
          tools:layout="@layout/fragment_home"&gt;
          &lt;action
              android:id="@+id/action_fragment_home_to_fragment_dialog_new_user_welcome"
              app:destination="@id/fragment_dialog_new_user_welcome"
              app:enterAnim="@anim/nav_fade_enter_anim"
              app:exitAnim="@anim/nav_fade_exit_anim"
              app:popUpTo="@layout/fragment_home" /&gt;
      &lt;/fragment&gt;
  
      &lt;dialog
          android:id="@+id/fragment_dialog_new_user_welcome"
          android:name="com.my.project.fragments.NewUserWelcomeDialog"
          tools:layout="@layout/fragment_dialog_new_user_welcome"&gt;
  
          &lt;action
              android:id="@+id/action_fragment_dialog_new_user_welcome_to_activity_discover_detail"
              app:destination="@id/fragment_discover_detail"
              app:launchSingleTop="true"
              app:popUpTo="@id/fragment_home" /&gt;
      &lt;/dialog&gt;
  </code></pre>
  
  <p>Here's the enter anim:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;set xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;alpha
          android:duration="1000"
          android:fromAlpha="0.0"
          android:toAlpha="1.0" /&gt;
  &lt;/set&gt;
  </code></pre>
  
  <p>Here's the exit anim:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;set xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;alpha
          android:duration="500"
          android:fromAlpha="1.0"
          android:toAlpha="0.0" /&gt;
  &lt;/set&gt;
  </code></pre>