Add a method to compare the keys of two QMaps

Hi,

I am using this code :

QMap<T, U> map1;
QMap<T, U> map2;
if (map1.keys() == map2.keys())
{
    // ...
}

It works perfectly, but when I analyze it with clazy, I get a "container-anti-pattern" warning, because "keys()" allocates and fills a new container, which is not needed to do this kind of comparison.
I talked about it with the clazy maintainer, who told me I could use :

bool keysEqual(const QMap<T, U> &map1, const QMap<T, U> &map2)
{
    if (map1.size() != map2.size())
        return false;

    for (auto it1 = map1.keyBegin(), it2 = map2.keyBegin(), e1 = map1.keyEnd(); it1 != e1; ++it1, ++it2) {
        if (*it1 != *it2)
            return false;
    }

    return true;
}

Which is a couple orders of magnitude faster.

So, I think it would be interesting to add this kind of method in QMap itself (and maybe other containers as well)