rbutil: More Qt6 compatibility.

Qt6 doesn't contain QTextCodec anymore but instead provides it in the
optional core5compat module.

Change-Id: Ia45985a32df3826faf041981b8935c839946e5c9

rbutil/rbutilqt/quazip/quazip.h

@@ -27,7 +27,7 @@ quazip/(un)zip.h files for details, basically it's zlib license.
 
 #include <QtCore/QString>
 #include <QtCore/QStringList>
-#include <QtCore/QTextCodec>
+#include <QTextCodec>
 
 #include "zip.h"
 #include "unzip.h"

rbutil/rbutilqt/rbutilqt.pro

@@ -161,6 +161,9 @@ QT += widgets
 if (lessThan(QT_MAJOR_VERSION, 6)) {
     QT += multimedia
 }
+if (greaterThan(QT_MAJOR_VERSION, 5)) {
+    QT += core5compat
+}
 
 CONFIG += c++11
 

rbutil/rbutilqt/themesinstallwindow.cpp

@@ -18,6 +18,7 @@
 
 #include <QDialog>
 #include <QMessageBox>
+#include <QTextCodec>
 
 #include "ui_themesinstallfrm.h"
 #include "themesinstallwindow.h"