wayland: Evaluate WINDOWPOS_CENTERED_DISPLAY for move events

Partially fixes the mouse cursor in UE5 editor. Imperfect because UE5 uses window position and global mouse state to get position, but of course we don't have global mouse and this is just to get the right display index so this still fails overall. We really need to make global mouse support a feature query...

src/video/wayland/SDL_waylandwindow.c

@@ -815,9 +815,12 @@ Wayland_move_window(SDL_Window *window,
     int i, numdisplays = SDL_GetNumVideoDisplays();
     for (i = 0; i < numdisplays; i += 1) {
         if (SDL_GetDisplay(i)->driverdata == driverdata) {
+            /* Equivalent of SDL_WINDOWPOS_CENTERED_DISPLAY(i) */
+            SDL_Rect bounds;
+            SDL_GetDisplayBounds(i, &bounds);
             SDL_SendWindowEvent(window, SDL_WINDOWEVENT_MOVED,
-                                SDL_WINDOWPOS_CENTERED_DISPLAY(i),
-                                SDL_WINDOWPOS_CENTERED_DISPLAY(i));
+                                bounds.x + (bounds.w - window->w) / 2,
+                                bounds.y + (bounds.h - window->h) / 2);
             break;
         }
     }