fix: [1/2] Keyboard Layout applet doesn't follow actual layout switching

We need to emit DBus signal on every layout change - explicit(keyboard shortcut, layout applet click)
and implicit(focus window with different layout).
Otherwise, external layout applet might not get updated.

DIGEST:
BUG: 426900

keyboard_layout_switching.cpp

@@ -38,6 +38,7 @@ void Policy::setLayout(quint32 layout)
     m_xkb->switchToLayout(layout);
     if (previousLayout != m_xkb->currentLayout()) {
         m_layout->updateNotifier();
+        emit m_layout->layoutChanged();
     }
 }