Give Audio{De,En}coderIsac* an "Impl" suffix, to free up the original names

webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "webrtc/modules/audio_coding/codecs/isac/fix/include/audio_decoder_isacfix.h"
 #include "webrtc/test/fuzzers/audio_decoder_fuzzer.h"
 
 namespace webrtc {
 void FuzzOneInput(const uint8_t* data, size_t size) {
   static const int kSampleRateHz = 16000;
   static const size_t kAllocatedOuputSizeSamples = 16000 / 10;  // 100 ms.
   int16_t output[kAllocatedOuputSizeSamples];
-  AudioDecoderIsacFix dec(kSampleRateHz);
+  AudioDecoderIsacFixImpl dec(kSampleRateHz);
   FuzzAudioDecoder(DecoderFunctionType::kNormalDecode, data, size, &dec,
                    kSampleRateHz, sizeof(output), output);
 }
 }  // namespace webrtc