Added an API to get the type of a connected joystick

src/joystick/SDL_sysjoystick.h

@@ -62,6 +62,7 @@ struct _SDL_Joystick
 
     int ref_count;              /* Reference count for multiple opens */
 
+    SDL_bool is_game_controller;
     SDL_bool force_recentering; /* SDL_TRUE if this device needs to have its state reset to 0 */
     SDL_JoystickPowerLevel epowerlevel; /* power level of this joystick, SDL_JOYSTICK_POWER_UNKNOWN if not supported */
     struct _SDL_Joystick *next; /* pointer to next joystick we have allocated */