Adopt absl::string_view in modules/audio_coding/

Bug: webrtc:13579
Change-Id: Ifec66fb6ba9724d18539de7245a358c2d13c7939
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/268547
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Ali Tofigh <alito@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37573}

modules/audio_coding/test/TestVADDTX.h

@@ -13,6 +13,7 @@
 
 #include <memory>
 
+#include "absl/strings/string_view.h"
 #include "api/audio_codecs/audio_decoder_factory.h"
 #include "api/audio_codecs/audio_encoder_factory.h"
 #include "common_audio/vad/include/vad.h"
@@ -73,10 +74,10 @@ class TestVadDtx {
   // 0 - kEmptyFrame
   // 1 - kAudioFrameSpeech
   // 2 - kAudioFrameCN
-  void Run(std::string in_filename,
+  void Run(absl::string_view in_filename,
            int frequency,
            int channels,
-           std::string out_filename,
+           absl::string_view out_filename,
            bool append,
            const int* expects);