qt6: nglcompression, widgets, dialog fixes: remove QTextCodec, QStringRef/splitRef, QDesktopWidget, use QMultiMap and Qt6 APIs; adjust QtConcurrent::run wrappers; replace endl with newline

Z/src/nglsettings/nglsettings_settings.cpp

@@ -166,9 +166,9 @@ namespace NGL
     QString defaultPw = QStringLiteral("ctc11de");
     if (!databaseUser.isEmpty())
     {
-      const QVector<QStringRef> &sl = databaseUser.splitRef(QLatin1Char('_'));
-      if (sl.size() > 1)
-        defaultPw = sl.at(0).toString() + QStringLiteral("11de");
+      const QStringList sl = databaseUser.split(QLatin1Char('_'));
+      if (!sl.isEmpty())
+        defaultPw = sl.at(0) + QStringLiteral("11de");
     }
     return m_settings->value(QLatin1String("db/passwd"), defaultPw).toString();
   }