wayland: Expose wl_output objects on video displays

Some protocols take a wl_output object to function, so expose them via a property on the video displays.

src/video/SDL_video.c

@@ -855,6 +855,7 @@ SDL_DisplayID SDL_AddVideoDisplay(const SDL_VideoDisplay *display, bool send_eve
     SDL_copyp(new_display, display);
     new_display->id = id;
     new_display->device = _this;
+    new_display->props = display->props;
     if (display->name) {
         new_display->name = SDL_strdup(display->name);
     } else {

src/video/wayland/SDL_waylandvideo.c

@@ -1071,6 +1071,9 @@ static void display_handle_done(void *data,
         internal->placeholder.current_orientation = internal->orientation;
         internal->placeholder.internal = internal;
 
+        internal->placeholder.props = SDL_CreateProperties();
+        SDL_SetPointerProperty(internal->placeholder.props, SDL_PROP_DISPLAY_WAYLAND_WL_OUTPUT_POINTER, internal->output);
+
         // During initialization, the displays will be added after enumeration is complete.
         if (!video->initializing) {
             internal->display = SDL_AddVideoDisplay(&internal->placeholder, true);