Workaround what appear to be QStringConverter bugs

* Data modification when using QStringConverter::encodingForData
  (QTBUG-87466)

* Crash when calling QStringDecoder::decode (not reported yet, unsure
  what causes it).

For now we assume scripts are saved as UTF-8 when compiling against
Qt 6.

src/tiled/scriptmanager.cpp

@@ -178,13 +178,15 @@ QJSValue ScriptManager::evaluateFile(const QString &fileName)
     if (!fromUtf8(bytes, script))
         script = QTextCodec::codecForUtfText(bytes)->toUnicode(bytes);
 #else
-    auto encoding = QStringConverter::encodingForData(bytes.constData(), bytes.size());
-    QStringDecoder decoder(encoding.value_or(QStringConverter::Encoding::Utf8));
-    script = decoder.decode(bytes);
-    if (decoder.hasError()) {
-        Tiled::ERROR(tr("Error decoding file: %1").arg(fileName));
-        return QJSValue();
-    }
+    // Workaround for Qt 6.0 Alpha bug (QTBUG-87466)
+//    auto encoding = QStringConverter::encodingForData(bytes.constData(), bytes.size());
+//    QStringDecoder decoder(encoding.value_or(QStringConverter::Encoding::Utf8));
+//    script = decoder.decode(bytes);
+//    if (decoder.hasError()) {
+//        Tiled::ERROR(tr("Error decoding file: %1").arg(fileName));
+//        return QJSValue();
+//    }
+    script = QString::fromUtf8(bytes);
 #endif
 
     Tiled::INFO(tr("Evaluating '%1'").arg(fileName));