Typedef `SDL_WindowFlags`

Window flags were previously an enum with the same name.
See ebd7f9adbd.

docs/README-migration.md

@@ -1680,7 +1680,6 @@ The following functions have been removed:
 * SDL_CreateWindowFrom() - use SDL_CreateWindowWithProperties() with the properties that allow you to wrap an existing window
 
 The SDL_Window id type is named SDL_WindowID
-The SDL_WindowFlags enum should be replaced with Uint32
 
 The following symbols have been renamed:
 * SDL_WINDOW_ALLOW_HIGHDPI => SDL_WINDOW_HIGH_PIXEL_DENSITY

include/SDL3/SDL_video.h

@@ -141,6 +141,8 @@ typedef struct SDL_Window SDL_Window;
  *
  *  \sa SDL_GetWindowFlags
  */
+typedef Uint32 SDL_WindowFlags;
+
 #define SDL_WINDOW_FULLSCREEN           0x00000001U /**< window is in fullscreen mode */
 #define SDL_WINDOW_OPENGL               0x00000002U /**< window usable with OpenGL context */
 #define SDL_WINDOW_OCCLUDED             0x00000004U /**< window is occluded */