kdecoration: Port to DecoratedClient::windowClass()

It removes the need for X11 and makes window class matching work on
wayland.

kdecoration/breezesettingsprovider.cpp

@@ -8,8 +8,6 @@
 
 #include "breezeexceptionlist.h"
 
-#include <KWindowInfo>
-
 #include <QRegularExpression>
 #include <QTextStream>
 
@@ -60,7 +58,7 @@ void SettingsProvider::reconfigure()
 InternalSettingsPtr SettingsProvider::internalSettings(Decoration *decoration) const
 {
     QString windowTitle;
-    QString className;
+    QString windowClass;
 
     // get the client
     const auto client = decoration->client().toStrongRef();
@@ -87,15 +85,7 @@ InternalSettingsPtr SettingsProvider::internalSettings(Decoration *decoration) c
 
         default:
         case InternalSettings::ExceptionWindowClassName: {
-            if (className.isEmpty()) {
-                // retrieve class name
-                KWindowInfo info(client->windowId(), {}, NET::WM2WindowClass);
-                QString window_className(QString::fromUtf8(info.windowClassName()));
-                QString window_class(QString::fromUtf8(info.windowClassClass()));
-                className = window_className + QStringLiteral(" ") + window_class;
-            }
-
-            value = className;
+            value = windowClass.isEmpty() ? (windowClass = client->windowClass()) : windowClass;
             break;
         }
         }