native-window-placement: update for gnome-shell API changes

St.Widget.get_default_direction() was replaced with
Clutter.get_default_text_direction() as part of the Clutter Apocalypses

extensions/native-window-placement/extension.js

@@ -434,7 +434,7 @@ function enable() {
 
             let settings = new Gio.Settings({ schema: BUTTON_LAYOUT_SCHEMA });
             let layout = settings.get_string(BUTTON_LAYOUT_KEY);
-            let rtl = St.Widget.get_default_direction() == St.TextDirection.RTL;
+            let rtl = Clutter.get_default_text_direction() == Clutter.TextDirection.RTL;
 
             let split = layout.split(":");
             let side;