[REG 5.15 -> 6] QList::op==() is broken for FP types

FP types are partially ordered, so comparison of containers that store NaN values should take it into consideration.
However, in practice we see that comparison of two QLists holding NaN values provides different results than simply comparing two NaN values:

QList<float> l1{std::numeric_limits<float>::quiet_NaN()};
QList<float> l2{std::numeric_limits<float>::quiet_NaN()};
qDebug() << (l1 == l2); // true
qDebug() << (l1.front() == l2.front()); // false

The reason for that is most probably qtbase/db89349bdba2fcc03b2f7e2d23f549a9ec5dc0e3 (https://codereview.qt-project.org/c/qt/qtbase/+/282602) which added an optimization that uses memcmp() for arithmetic types.