xwayland: Send a notification when Xwayland crashes

Send a notification when Xwayland crashes to provide the user some
feedback regarding why all X11 clients have disappeared.

kwin.notifyrc

@@ -287,3 +287,8 @@ Comment[x-test]=xxA graphics reset event occurredxx
 Comment[zh_CN]=发生了图形重置事件
 Comment[zh_TW]=發生了圖形重置事件
 Action=Popup
+
+[Event/xwaylandcrash]
+Name=Xwayland Crash
+Comment=Xwayland has crashed
+Action=Popup

xwl/xwayland.cpp

@@ -19,6 +19,7 @@
 #include "xwayland_logging.h"
 
 #include <KLocalizedString>
+#include <KNotification>
 #include <KSelectionOwner>
 
 #include <QAbstractEventDispatcher>
@@ -243,6 +244,7 @@ void Xwayland::handleXwaylandFinished(int exitCode, QProcess::ExitStatus exitSta
 
 void Xwayland::handleXwaylandCrashed()
 {
+    KNotification::event(QStringLiteral("xwaylandcrash"), i18n("Xwayland has crashed"));
     m_resetCrashCountTimer->stop();
 
     switch (options->xwaylandCrashPolicy()) {