Refactor audio buffering API, this should mainly prevent SDL audio driver from allocating memory in the mixer callback.

GpAudioDriver_XAudio2/GpAudioBufferXAudio2.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "IGpAudioBuffer.h"
+
+#include <xaudio2.h>
+
+class GpAudioBufferXAudio2 final : public IGpAudioBuffer
+{
+public:
+	static GpAudioBufferXAudio2 *Create(const void *buffer, size_t size);
+
+	void AddRef() override;
+	void Release() override;
+
+	const XAUDIO2_BUFFER *GetXA2Buffer() const;
+
+private:
+	GpAudioBufferXAudio2(const void *data, size_t size);
+	~GpAudioBufferXAudio2();
+
+	void Destroy();
+
+	const void *m_data;
+	size_t m_size;
+
+	XAUDIO2_BUFFER m_xa2Buffer;
+
+	volatile unsigned int m_count;
+};