Get the mapping of a game controller.
char* SDL_GameControllerMappingForDeviceIndex(int joystick_index);
the device_index of a device, from zero to SDL_NumJoysticks()-1
Returns the mapping string. Must be freed with SDL_free(). Returns NULL if no mapping is available.
This can be called before any controllers are opened.
This function is available since SDL 3.0.0.