Restructure the audioproc_f tool into a library with a thin executable wrapper.

This refactoring makes it easier to experiment with injectable components.

Bug: webrtc:8732
Change-Id: I2cd2a8ff80516a76aec814af02b61778915f2217
Reviewed-on: https://webrtc-review.googlesource.com/60863
Commit-Queue: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22372}

modules/audio_processing/test/wav_based_simulator.h

@@ -23,7 +23,8 @@ namespace test {
 // Used to perform an audio processing simulation from wav files.
 class WavBasedSimulator final : public AudioProcessingSimulator {
  public:
-  explicit WavBasedSimulator(const SimulationSettings& settings);
+  WavBasedSimulator(const SimulationSettings& settings,
+                    std::unique_ptr<AudioProcessingBuilder> ap_builder);
   ~WavBasedSimulator() override;
 
   // Processes the WAV input.