window-list: Force single-line window titles

While window titles really really shouldn't contain newline characters,
they are under application control and therefore may very well do.
Force the corresponding labels to be single line, to prevent offending
applications from messing up the whole window list layout.

https://gitlab.gnome.org/GNOME/gnome-shell-extensions/issues/202

extensions/window-list/extension.js

@@ -146,6 +146,7 @@ class WindowTitle extends St.BoxLayout {
         this._icon = new St.Bin({ style_class: 'window-button-icon' });
         this.add(this._icon);
         this.label_actor = new St.Label({ y_align: Clutter.ActorAlign.CENTER });
+        this.label_actor.clutter_text.single_line_mode = true;
         this.add(this.label_actor);
 
         this._textureCache = St.TextureCache.get_default();