Added SDL_PROP_WINDOW_CREATE_WINDOWSCENE_POINTER

This lets applications choose which scene their windows are being created in. For example one window might be video output in a scene with a session role of UIWindowSceneSessionRoleExternalDisplayNonInteractive, and video controls in a scene with a session role of UIWindowSceneSessionRoleApplication.

include/SDL3/SDL_video.h

@@ -1331,6 +1331,11 @@ extern SDL_DECLSPEC SDL_Window * SDLCALL SDL_CreatePopupWindow(SDL_Window *paren
  * - `SDL_PROP_WINDOW_CREATE_COCOA_VIEW_POINTER`: the `(__unsafe_unretained)`
  *   NSView associated with the window, defaults to `[window contentView]`
  *
+ * These are additional supported properties on iOS, tvOS, and visionOS:
+ *
+ * - `SDL_PROP_WINDOW_CREATE_WINDOWSCENE_POINTER`: the `(__unsafe_unretained)`
+ *   UIWindowScene associated with the window, defaults to the active window scene.
+ *
  * These are additional supported properties on Wayland:
  *
  * - `SDL_PROP_WINDOW_CREATE_WAYLAND_SURFACE_ROLE_CUSTOM_BOOLEAN` - true if
@@ -1439,6 +1444,7 @@ extern SDL_DECLSPEC SDL_Window * SDLCALL SDL_CreateWindowWithProperties(SDL_Prop
 #define SDL_PROP_WINDOW_CREATE_Y_NUMBER                            "SDL.window.create.y"
 #define SDL_PROP_WINDOW_CREATE_COCOA_WINDOW_POINTER                "SDL.window.create.cocoa.window"
 #define SDL_PROP_WINDOW_CREATE_COCOA_VIEW_POINTER                  "SDL.window.create.cocoa.view"
+#define SDL_PROP_WINDOW_CREATE_WINDOWSCENE_POINTER                 "SDL.window.create.uikit.windowscene"
 #define SDL_PROP_WINDOW_CREATE_WAYLAND_SURFACE_ROLE_CUSTOM_BOOLEAN "SDL.window.create.wayland.surface_role_custom"
 #define SDL_PROP_WINDOW_CREATE_WAYLAND_CREATE_EGL_WINDOW_BOOLEAN   "SDL.window.create.wayland.create_egl_window"
 #define SDL_PROP_WINDOW_CREATE_WAYLAND_WL_SURFACE_POINTER          "SDL.window.create.wayland.wl_surface"

src/video/uikit/SDL_uikitwindow.m

@@ -173,7 +173,10 @@ bool UIKit_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_Properti
 
         UIWindow *uiwindow = nil;
         if (@available(iOS 13.0, tvOS 13.0, *)) {
-            UIWindowScene *scene = UIKit_GetActiveWindowScene();
+            UIWindowScene *scene = (__bridge UIWindowScene *)SDL_GetPointerProperty(create_props, SDL_PROP_WINDOW_CREATE_WINDOWSCENE_POINTER, NULL);
+            if (!scene) {
+                scene = UIKit_GetActiveWindowScene();
+            }
             if (scene) {
                 uiwindow = [[UIWindow alloc] initWithWindowScene:scene];
             }