Decouple emulator and frontend code

include/panda_sdl/frontend_sdl.hpp

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <SDL.h>
+
+#include "emulator.hpp"
+
+struct FrontendSDL {
+	FrontendSDL();
+	bool loadROM(const std::filesystem::path& path);
+	void run();
+
+	Emulator emu;
+	SDL_Window* window = nullptr;
+#ifdef PANDA3DS_ENABLE_OPENGL
+	SDL_GLContext glContext;
+#endif
+	SDL_GameController* gameController = nullptr;
+	int gameControllerID;
+};