Fix withDecoderExtensions flavor detection in internal demo app

PiperOrigin-RevId: 322781213

demos/main/build.gradle

@@ -55,9 +55,11 @@ android {
     productFlavors {
         noDecoderExtensions {
             dimension "decoderExtensions"
+            buildConfigField "boolean", "USE_DECODER_EXTENSIONS", "false"
         }
         withDecoderExtensions {
             dimension "decoderExtensions"
+            buildConfigField "boolean", "USE_DECODER_EXTENSIONS", "true"
         }
     }
 }

demos/main/src/main/java/com/google/android/exoplayer2/demo/DemoUtil.java

@@ -61,7 +61,7 @@ public final class DemoUtil {
 
   /** Returns whether extension renderers should be used. */
   public static boolean useExtensionRenderers() {
-    return "withDecoderExtensions".equals(BuildConfig.FLAVOR);
+    return BuildConfig.USE_DECODER_EXTENSIONS;
   }
 
   public static RenderersFactory buildRenderersFactory(