[D3D12] Persistent shader and PSO storage

src/xenia/gpu/graphics_system.h

@@ -12,6 +12,7 @@
 
 #include <atomic>
 #include <memory>
+#include <string>
 #include <thread>
 
 #include "xenia/cpu/processor.h"
@@ -62,6 +63,9 @@ class GraphicsSystem {
 
   virtual void ClearCaches();
 
+  void InitializeShaderStorage(const std::wstring& storage_root,
+                               uint32_t title_id, bool blocking);
+
   void RequestFrameTrace();
   void BeginTracing();
   void EndTracing();