Add the flag requesting a fullscreen window for the current desktop

Property definitions

sdl2 $ SDLWindowFlags :: fullscreen_desktop
	# Add the flag requesting a fullscreen window for the current desktop
	fun fullscreen_desktop: SDLWindowFlags `{ return self | SDL_WINDOW_FULLSCREEN_DESKTOP; `}
lib/sdl2/sdl2_base.nit:176,2--177,90