core/window: Implement GInitable

Currently, we will notify the display about a new window being created
during the constructed phase of the GObject. During this time,
property-change notifications are frozen by GObject, so we'll emit a few
::notify signals only after the window-created signal, although
the actual property change happened before that.

This caused confusion in gnome-shell code where a notify::skip-taskbar =
true emission was seen when the property already was true inside a
window-created handler before.

In order to fix that that, we notify the window creation
post-construction
of the GObject on GInitable.init vfunc

Details
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6119#note_1598983
Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6119

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2703>

src/wayland/meta-window-wayland.c

@@ -908,11 +908,12 @@ meta_window_wayland_new (MetaDisplay        *display,
   MetaWindowWayland *wl_window;
   MetaWindow *window;
 
-  window = g_object_new (META_TYPE_WINDOW_WAYLAND,
-                         "display", display,
-                         "effect", META_COMP_EFFECT_CREATE,
-                         "surface", surface,
-                         NULL);
+  window = g_initable_new (META_TYPE_WINDOW_WAYLAND,
+                           NULL, NULL,
+                           "display", display,
+                           "effect", META_COMP_EFFECT_CREATE,
+                           "surface", surface,
+                           NULL);
   wl_window = META_WINDOW_WAYLAND (window);
   set_geometry_scale_for_window (wl_window, wl_window->geometry_scale);