add SDL_RETURN_IF_ERROR, refactor bitmap

src/app/gfx/bitmap.h

@@ -87,6 +87,9 @@ class Bitmap {
     }
   }
 
+  std::vector<uint8_t> GetPngData();
+  void SaveSurfaceToFile(std::string_view filename);
+
   /**
    * @brief Creates a bitmap object with the provided graphical data.
    */
@@ -110,12 +113,6 @@ class Bitmap {
   void CreateTexture(SDL_Renderer *renderer);
   void UpdateTexture(SDL_Renderer *renderer, bool use_sdl_update = false);
 
-  void SaveSurfaceToFile(std::string_view filename);
-  void SetSurface(SDL_Surface *surface);
-  std::vector<uint8_t> GetPngData();
-  void LoadFromPngData(const std::vector<uint8_t> &png_data, int width,
-                       int height);
-
   /**
    * @brief Copy color data from the SnesPalette into the SDL_Palette
    */