Make it clear that you can't mix 2D rendering and the window surface API

Also added functions to query and destroy the window surface so you can switch between modes if you want.

See https://github.com/pygame-community/pygame-ce/issues/2190 for more details.

src/render/SDL_render.c

@@ -950,6 +950,11 @@ SDL_Renderer *SDL_CreateRenderer(SDL_Window *window, int index, Uint32 flags)
         goto error;
     }
 
+    if (SDL_HasWindowSurface(window)) {
+        SDL_SetError("Surface already associated with window");
+        goto error;
+    }
+
     if (SDL_GetRenderer(window)) {
         SDL_SetError("Renderer already associated with window");
         goto error;