Register unique service name when wayland keyboard interface is in use

A situation meant we want to only enable the new keyboard applet by
default on wayland, using the legacy one from the X11 daemon on X11.

We need a unique service name so that we can use DBus activation on it.

keyboard_layout.cpp

@@ -176,6 +176,8 @@ void KeyboardLayout::notifyLayoutChange()
 }
 
 static const QString s_keyboardService = QStringLiteral("org.kde.keyboard");
+// this exists because in Plasma 5.21 we want to use a new applet for wayland, but still have the legacy system in use on X11
+static const QString s_keyboardService_appletTrigger = QStringLiteral("org.kde.keyboard.wayland");
 static const QString s_keyboardObject = QStringLiteral("/Layouts");
 
 KeyboardLayoutDBusInterface::KeyboardLayoutDBusInterface(Xkb *xkb, const KConfigGroup &configGroup, KeyboardLayout *parent)
@@ -190,11 +192,13 @@ KeyboardLayoutDBusInterface::KeyboardLayoutDBusInterface(Xkb *xkb, const KConfig
 
     QDBusConnection::sessionBus().registerObject(s_keyboardObject, this, QDBusConnection::ExportAllSlots | QDBusConnection::ExportAllSignals);
     QDBusConnection::sessionBus().registerService(s_keyboardService);
+    QDBusConnection::sessionBus().registerService(s_keyboardService_appletTrigger);
 }
 
 KeyboardLayoutDBusInterface::~KeyboardLayoutDBusInterface()
 {
     QDBusConnection::sessionBus().unregisterService(s_keyboardService);
+    QDBusConnection::sessionBus().unregisterService(s_keyboardService_appletTrigger);
 }
 
 void KeyboardLayoutDBusInterface::switchToNextLayout()