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.

include/SDL_video.h

@@ -1275,6 +1275,17 @@ extern DECLSPEC void SDLCALL SDL_RestoreWindow(SDL_Window * window);
 extern DECLSPEC int SDLCALL SDL_SetWindowFullscreen(SDL_Window * window,
                                                     Uint32 flags);
 
+/**
+ * Return whether the window has a surface associated with it.
+ *
+ * \returns SDL_TRUE if there is a surface associated with the window, or SDL_FALSE otherwise.
+ *
+ * \since This function is available since SDL 2.28.0.
+ *
+ * \sa SDL_GetWindowSurface
+ */
+extern DECLSPEC SDL_bool SDLCALL SDL_HasWindowSurface(SDL_Window *window);
+
 /**
  * Get the SDL surface associated with the window.
  *
@@ -1295,6 +1306,8 @@ extern DECLSPEC int SDLCALL SDL_SetWindowFullscreen(SDL_Window * window,
  *
  * \since This function is available since SDL 2.0.0.
  *
+ * \sa SDL_DestroyWindowSurface
+ * \sa SDL_HasWindowSurface
  * \sa SDL_UpdateWindowSurface
  * \sa SDL_UpdateWindowSurfaceRects
  */
@@ -1343,6 +1356,20 @@ extern DECLSPEC int SDLCALL SDL_UpdateWindowSurfaceRects(SDL_Window * window,
                                                          const SDL_Rect * rects,
                                                          int numrects);
 
+/**
+ * Destroy the surface associated with the window.
+ *
+ * \param window the window to update
+ * \returns 0 on success or a negative error code on failure; call
+ *          SDL_GetError() for more information.
+ *
+ * \since This function is available since SDL 2.28.0.
+ *
+ * \sa SDL_GetWindowSurface
+ * \sa SDL_HasWindowSurface
+ */
+extern DECLSPEC int SDLCALL SDL_DestroyWindowSurface(SDL_Window *window);
+
 /**
  * Set a window's input grab mode.
  *