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

webrtc/test/fuzzers/audio_decoder_isac_fuzzer.cc

Index: webrtc/test/fuzzers/audio_decoder_isac_fuzzer.cc
diff --git a/webrtc/test/fuzzers/audio_decoder_isac_fuzzer.cc b/webrtc/test/fuzzers/audio_decoder_isac_fuzzer.cc
index b013a346176c42f74bcba676e62af13b7f7ee71a..10227763f7ecd5386e528f6cc27ed4956f29b914 100644
--- a/webrtc/test/fuzzers/audio_decoder_isac_fuzzer.cc
+++ b/webrtc/test/fuzzers/audio_decoder_isac_fuzzer.cc
@@ -16,7 +16,7 @@ void FuzzOneInput(const uint8_t* data, size_t size) {
   const int sample_rate_hz = size % 2 == 0 ? 16000 : 32000;     // 16 or 32 kHz.
   static const size_t kAllocatedOuputSizeSamples = 32000 / 10;  // 100 ms.
   int16_t output[kAllocatedOuputSizeSamples];
-  AudioDecoderIsac dec(sample_rate_hz);
+  AudioDecoderIsacFloatImpl dec(sample_rate_hz);
   FuzzAudioDecoder(DecoderFunctionType::kNormalDecode, data, size, &dec,
                    sample_rate_hz, sizeof(output), output);
 }