title: Android manifest activity name generates a RunTime exception
body: <p>Trying to name an <code>activity</code> in my Android.manifest file following the docs <a href="https://developer.android.com/guide/topics/manifest/activity-element" rel="nofollow noreferrer">here</a>:</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;manifest 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:versionCode="1"
    android:versionName="1.0"
    package="com.companyname.xamarinauth"
  &gt;
      &lt;uses-sdk android:minSdkVersion="21" android:targetSdkVersion="28" /&gt;
      &lt;application android:label="XamarinAuth.Android" &gt;
  
        &lt;activity android:name=".MainActivity"&gt;
  
          &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.MAIN" /&gt;
            &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
          &lt;/intent-filter&gt;
  
          &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.VIEW" /&gt;
            &lt;category android:name="android.intent.category.DEFAULT" /&gt;
            &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
            &lt;data android:scheme="obsolete-scheme" /&gt;
          &lt;/intent-filter&gt;
        &lt;/activity&gt;
  
      &lt;/application&gt;
  
    &lt;uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /&gt;
  &lt;/manifest&gt;
  </code></pre>
  
  <p>No matter what class name or string I provide to the activity's name property I get a run time exception:</p>
  
  <pre><code>**Java.Lang.RuntimeException:** 'Unable to instantiate activity ComponentInfo{com.companyname.xamarinauth/com.companyname.xamarinauth.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.companyname.xamarinauth.MainActivity" on path: DexPathList[[zip file "/data/app/com.companyname.xamarinauth-LAUvw_T2YXTzpe7rXmRWhg==/base.apk"],nativeLibraryDirectories=[/data/app/com.companyname.xamarinauth-LAUvw_T2YXTzpe7rXmRWhg==/lib/arm64, /data/app/com.companyname.xamarinauth-LAUvw_T2YXTzpe7rXmRWhg==/base.apk!/lib/arm64-v8a, /system/lib64]]
  </code></pre>
  
  <p>The boilerplate Xamarin code generated by Visual Studio creates the MainActivity class for me:</p>
  
  <pre class="lang-cs prettyprint-override"><code>    [Activity(
          Label = "XamarinAuth",
          Icon = "@mipmap/icon",
          Theme = "@style/MainTheme",
          MainLauncher = true, 
          ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation
          )]
      public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
  {...}
  </code></pre>
  
  <p>I am assuming <code>FormsAppCompatActivity</code> is a subclass of <code>Activity</code>? Providing a name of any variation on the theme of <code>com.companyname.xamarinauth.MainActivity</code> generates the error. What am I missing?</p>