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

webrtc/modules/audio_coding/codecs/isac/fix/include/audio_decoder_isacfix.h

 /*
  *  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.
  */
 
 #ifndef WEBRTC_MODULES_AUDIO_CODING_CODECS_ISAC_FIX_INCLUDE_AUDIO_DECODER_ISACFIX_H_
 #define WEBRTC_MODULES_AUDIO_CODING_CODECS_ISAC_FIX_INCLUDE_AUDIO_DECODER_ISACFIX_H_
 
 #include "webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h"
 #include "webrtc/modules/audio_coding/codecs/isac/fix/source/isac_fix_type.h"
 
 namespace webrtc {
 
-using AudioDecoderIsacFix = AudioDecoderIsacT<IsacFix>;
+using AudioDecoderIsacFixImpl = AudioDecoderIsacT<IsacFix>;
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_ISAC_FIX_INCLUDE_AUDIO_DECODER_ISACFIX_H_