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

webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc

Index: webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc
diff --git a/webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc b/webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc
index 25ab3f454ded804a2908204440f3e7dd8d8daa91..64cdccb2fc9b702aa856f80d7ec4d9340058bff7 100644
--- a/webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc
+++ b/webrtc/test/fuzzers/audio_decoder_isacfix_fuzzer.cc
@@ -16,7 +16,7 @@ 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);
 }