VideoCommon: add custom includer to custom shaders, this will allow us to ship built-in custom shaders in the future

Source/Core/VideoCommon/Assets/DirectFilesystemAssetLibrary.cpp

@@ -8,6 +8,7 @@
 
 #include <fmt/std.h>
 
+#include "Common/CommonPaths.h"
 #include "Common/FileUtil.h"
 #include "Common/IOFile.h"
 #include "Common/JsonUtil.h"
@@ -150,6 +151,12 @@ DirectFilesystemAssetLibrary::LoadRasterSurfaceShader(const AssetID& asset_id,
   if (!RasterSurfaceShaderData::FromJson(asset_id, root_obj, data))
     return {};
 
+  const std::string graphics_mod_builtin =
+      File::GetSysDirectory() + GRAPHICSMOD_DIR + "/Builtin" + "/Shaders";
+
+  data->shader_includer = std::make_unique<VideoCommon::ShaderIncluder>(
+      PathToString(pixel_shader->second.parent_path()), graphics_mod_builtin);
+
   return LoadInfo{approx_mem_size};
 }