appMenu: Only show 'Quit' for running apps

The top bar menu always corresponds to a running app, so it made
sense to include the 'Quit' item unconditionally. That won't be
the case for the overview context menus, so handle app state changes
and show/hide the item as necessary.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1948>

js/ui/appMenu.js

@@ -71,6 +71,7 @@ var AppMenu = class AppMenu extends PopupMenu.PopupMenu {
 
         this.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
 
+        this._quitItem =
             this.addAction(_('Quit'), () => this._app.request_quit());
 
         this._signals = [];
@@ -78,10 +79,26 @@ var AppMenu = class AppMenu extends PopupMenu.PopupMenu {
             this._appSystem,
             this._appSystem.connect('installed-changed',
                 () => this._updateDetailsVisibility()),
+        ], [
+            this._appSystem,
+            this._appSystem.connect('app-state-changed',
+                this._onAppStateChanged.bind(this)),
         ]);
+        this._updateQuitItem();
         this._updateDetailsVisibility();
     }
 
+    _onAppStateChanged(sys, app) {
+        if (this._app !== app)
+            return;
+
+        this._updateQuitItem();
+    }
+
+    _updateQuitItem() {
+        this._quitItem.visible = this._app?.state === Shell.AppState.RUNNING;
+    }
+
     _updateDetailsVisibility() {
         const sw = this._appSystem.lookup_app('org.gnome.Software.desktop');
         this._detailsItem.visible = sw !== null;
@@ -149,6 +166,7 @@ var AppMenu = class AppMenu extends PopupMenu.PopupMenu {
 
         this._newWindowItem.visible =
             app && app.can_open_new_window() && !actions.includes('new-window');
+        this._updateQuitItem();
     }
 
     _queueUpdateWindowsSection() {