Decide whether QV4::Sequence should be implicitly convertable to QStringList

https://bugs.kde.org/show_bug.cgi?id=488558 shows a case where a QJsonArray was implicitly converted to QStringList via JavaScript Array in Qt 6.7. This doesn't work anymore because since https://codereview.qt-project.org/c/qt/qtdeclarative/+/561082 a QJsonArray is represented as QV4::Sequence, not as JS Array.

So the underlying question is whether we should implicitly coerce array-likes to QStringList (via element-wise ToString). If so, this should work with all array-likes. If not, it should also not work for JavaScript arrays.