title: Android ViewBinding with CustomView
body: <p>I'd like to use try out the ViewBinding with custom view, for example:</p>
  
  <pre><code>MainActivity &lt;=&gt; layout_main.xml
  MyCustomView &lt;=&gt; layout_my_custom_view.xml
  </code></pre>
  
  <p>layout_main.xml</p>
  
  <pre><code>&lt;FrameLayout
          xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="match_parent"
          android:layout_height="match_parent"&gt;
  
          &lt;com.example.myapplication.MyCustomView
              android:id="@+id/custom_view"
              android:layout_width="match_parent"
              android:layout_height="match_parent" /&gt;
  &lt;/FrameLayout&gt;
  </code></pre>
  
  <p>layout_my_custom_view.xml</p>
  
  <pre><code>&lt;LinearLayout
          xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical"&gt;
  
          &lt;TextView
              android:id="@+id/line1"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:text="Line1" /&gt;
  
          &lt;View
              android:id="@+id/divider"
              android:layout_width="match_parent"
              android:layout_height="2dp"
              android:background="#2389bb" /&gt;
  
          &lt;TextView
              android:id="@+id/line2"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:text="Line2" /&gt;
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>MainActivity</p>
  
  <pre><code>class MainActivity : AppCompatActivity() {
  
      private lateinit var binding: LayoutMainBinding
  
      override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          binding = LayoutMainBinding.inflate(layoutInflater)
          setContentView(binding.root)
  
          binding.customView.line1.text = "Hello"
          binding.customView.line2.text = "World"
      }
  }
  </code></pre>
  
  <p>In my MainActivity, I can use the binding to find MyCustomView but I can't further find <code>@id/line1</code> and <code>@id/line2</code> in MyCustomView. In this case, is it possible to use ViewBinding only or do I have to use <code>findViewById</code> or Kotlin synthetic ??</p>
  
  <p>Thanks in advance.</p>