[ci skip] Add macOS native Audio Backend (ryubing/ryujinx!252)

See merge request ryubing/ryujinx!252

THIS IS CURRENTLY NOT EXPOSED BY THE UI OR HANDLED BY THE EMULATOR. Expect a commit later to add it to configs, UI, etc.

src/Ryujinx.Audio.Backends.Apple/AppleAudioBuffer.cs

@@ -0,0 +1,16 @@
+namespace Ryujinx.Audio.Backends.Apple
+{
+    class AppleAudioBuffer
+    {
+        public readonly ulong DriverIdentifier;
+        public readonly ulong SampleCount;
+        public ulong SamplePlayed;
+
+        public AppleAudioBuffer(ulong driverIdentifier, ulong sampleCount)
+        {
+            DriverIdentifier = driverIdentifier;
+            SampleCount = sampleCount;
+            SamplePlayed = 0;
+        }
+    }
+}