Pass CapturingDecoderFactory to AssetLoader

Otherwise, the decoders are not captured. It works at the moment for the
video decoder because decoding is still done on the sample pipeline but
it will moved to the AssetLoader soon.

PiperOrigin-RevId: 495275575

libraries/transformer/src/main/java/androidx/media3/transformer/TransformerInternal.java

@@ -160,7 +160,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
             .setRemoveVideo(removeVideo)
             .setFlattenVideoForSlowMotion(transformationRequest.flattenForSlowMotion)
             .setMediaSourceFactory(mediaSourceFactory)
-            .setDecoderFactory(decoderFactory)
+            .setDecoderFactory(this.decoderFactory)
             .setLooper(internalLooper)
             .setListener(componentListener)
             .setClock(clock)