audio_core: Add interfaces for Sink and SinkStream.

src/audio_core/null_sink.h

@@ -0,0 +1,27 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "audio_core/sink.h"
+
+namespace AudioCore {
+
+class NullSink final : public Sink {
+public:
+    explicit NullSink(std::string){};
+    ~NullSink() override = default;
+
+    SinkStream& AcquireSinkStream(u32 /*sample_rate*/, u32 /*num_channels*/) override {
+        return null_sink_stream;
+    }
+
+private:
+    struct NullSinkStreamImpl final : SinkStream {
+        void EnqueueSamples(u32 /*num_channels*/, const s16* /*samples*/,
+                            size_t /*sample_count*/) override {}
+    } null_sink_stream;
+};
+
+} // namespace AudioCore