Folded SDL_WINDOW_FULLSCREEN_EXCLUSIVE and SDL_WINDOW_FULLSCREEN_DESKTOP into a single SDL_WINDOW_FULLSCREEN flag

The fullscreen video mode used by the window can be used to determine whether it's in exclusive fullscreen or fullscreen desktop mode.

include/SDL3/SDL_test_common.h

@@ -80,6 +80,7 @@ typedef struct
     float scale;
     int depth;
     float refresh_rate;
+    SDL_bool fullscreen_exclusive;
     SDL_DisplayMode fullscreen_mode;
     int num_windows;
     SDL_Window **windows;