[kcm/common] Port EffectsModel away from KPluginMetaData::metaDataFileName

It's gone in KF6

It's only used to obtain the install location of the package and resolve files relative to that

Use QStandardPaths to locate those files directly

src/kcms/common/effectsmodel.cpp

@@ -312,10 +312,8 @@ void EffectsModel::loadJavascriptEffects(const KConfigGroup &kwinConfig)
 
         const QString pluginKeyword = plugin.value(QStringLiteral("X-KDE-PluginKeyword"));
         if (!pluginKeyword.isEmpty()) {
-            QDir package(QFileInfo(plugin.metaDataFileName()).dir());
-            package.cd(QStringLiteral("contents"));
-            const QString xmlFile = package.filePath(QStringLiteral("config/main.xml"));
-            const QString uiFile = package.filePath(QStringLiteral("ui/config.ui"));
+            const QString xmlFile = QStandardPaths::locate(QStandardPaths::GenericDataLocation, QLatin1String("kwin/effects/") + plugin.pluginId() + QLatin1String("/contents/config/main.xml"));
+            const QString uiFile = QStandardPaths::locate(QStandardPaths::GenericDataLocation, QLatin1String("kwin/effects/") + plugin.pluginId() + QLatin1String("/contents/ui/config.ui"));
             effect.configurable = QFileInfo::exists(xmlFile) && QFileInfo::exists(uiFile);
         } else {
             effect.configurable = false;