[media] Reset audio decoder via AudioDecoder::Reset() (#2672)

1. When AdaptiveAudioDecoder() resets |audio_decoder_|, use
audio_decoder_->Reset() to reset |audio_decoder_|.
2. The PR (#2501) does not clean
up |resampler_| and |channel_mixer_|, which causes some tests failed on
ps5. This PR cleans up |resampler_| and |channel_mixer_| in
AdaptiveAudioDecoder::Reset() to fix the
SbPlayerGetAudioConfigurationTest.MultipleSeeks test failures.

b/327229953

starboard/shared/starboard/player/filter/adaptive_audio_decoder_internal.cc

@@ -147,6 +147,8 @@ void AdaptiveAudioDecoder::Reset() {
 
   if (audio_decoder_) {
     audio_decoder_->Reset();
+    resampler_.reset();
+    channel_mixer_.reset();
   }
   CancelPendingJobs();
   while (!decoded_audios_.empty()) {