Switch incorrectly configured native multidex to legacy for demos

Native multidex can only be used for binaries with minSdkVersion of 21 or higher, but minSdkVersion was specified to 16.

PiperOrigin-RevId: 470004102
(cherry picked from commit a395b23d)

demos/cast/src/main/AndroidManifest.xml

@@ -22,8 +22,13 @@
 
   <uses-sdk/>
 
-  <application android:label="@string/application_name" android:icon="@mipmap/ic_launcher"
-      android:largeHeap="true" android:allowBackup="false">
+  <application
+      android:name="androidx.multidex.MultiDexApplication"
+      android:label="@string/application_name"
+      android:icon="@mipmap/ic_launcher"
+      android:largeHeap="true"
+      android:allowBackup="false"
+      android:taskAffinity="">
 
     <meta-data android:name="com.google.android.gms.cast.framework.OPTIONS_PROVIDER_CLASS_NAME"
         android:value="com.google.android.exoplayer2.ext.cast.DefaultCastOptionsProvider"/>

demos/gl/build.gradle

@@ -52,6 +52,7 @@ dependencies {
     implementation project(modulePrefix + 'library-smoothstreaming')
     implementation project(modulePrefix + 'library-ui')
     implementation 'androidx.annotation:annotation:' + androidxAnnotationVersion
+    implementation 'androidx.multidex:multidex:' + androidxMultidexVersion
     compileOnly 'org.checkerframework:checker-qual:' + checkerframeworkVersion
     compileOnly 'org.checkerframework:checker-compat-qual:' + checkerframeworkCompatVersion
 }

demos/gl/src/main/AndroidManifest.xml

@@ -22,6 +22,7 @@
   <uses-sdk/>
 
   <application
+      android:name="androidx.multidex.MultiDexApplication"
       android:allowBackup="false"
       android:icon="@mipmap/ic_launcher"
       android:label="@string/application_name">