Instead of hiding the Plugins menu, show a "no plugins available" action

E.g. https://bugs.kde.org/show_bug.cgi?id=186382

This reverts 8ee53cc5.

src/Application.cpp

@@ -121,18 +121,7 @@ MainWindow *Application::newMainWindow()
     connect(window, &Konsole::MainWindow::newWindowRequest, this, &Konsole::Application::createWindow);
     connect(window, &Konsole::MainWindow::terminalsDetached, this, &Konsole::Application::detachTerminals);
 
-    if (!m_pluginManager.plugins().empty()) {
-        m_pluginManager.registerMainWindow(window);
-    } else {
-        const QList<QAction *> allActions = window->menuBar()->actions();
-        auto it = std::find_if(allActions.cbegin(), allActions.cend(), [](QAction *action) {
-            return action->objectName() == QLatin1String("plugins");
-        });
-
-        if (it != allActions.cend()) {
-            (*it)->setVisible(false);
-        }
-    }
+    m_pluginManager.registerMainWindow(window);
 
     return window;
 }

src/pluginsystem/PluginManager.cpp

@@ -10,9 +10,12 @@
 #include "IKonsolePlugin.h"
 #include "MainWindow.h"
 
+#include <KLocalizedString>
 #include <KPluginLoader>
 #include <KPluginMetaData>
 
+#include <QAction>
+
 namespace Konsole
 {
 struct PluginManagerPrivate {
@@ -59,6 +62,12 @@ void PluginManager::registerMainWindow(Konsole::MainWindow *window)
         window->addPlugin(plugin);
     }
 
+    if (internalPluginSubmenus.isEmpty()) {
+        auto *emptyMenuAct = new QAction(i18n("No plugins available"), this);
+        emptyMenuAct->setEnabled(false);
+        internalPluginSubmenus.append(emptyMenuAct);
+    }
+
     window->plugActionList(QStringLiteral("plugin-submenu"), internalPluginSubmenus);
 }