Q(Multi)Hash is missing range-erase()

Q(Multi)Hash, unlike all other Qt containers, and unlike std::unordered_map, lacks the erase(it, it) function ("range-erase"). Currently, the only option to erase a range of items in QHash is to loop over erase(it), which, however, has algorithmic complexity problems (see QTBUG-103328), so esp. when the range consists of equivalent elements (think QMultiHash), the erase(it) loop is necessarily quadratic.

Workaround: use removeIf() and hope for QTBUG-103328 to be fixed.

Acceptance criteria: The following test passes and has complexity linear in N = std::distance(b, e):

QMultiHash<int, QString> h = {
    {0, "zero"},
    {1, "one"},
    {1, "uno"},
    {2, "two"},
};
auto b = h.find(1);
auto e = std::next(b);
auto it  = h.erase(b, e);
static_assert(std::is_same_v<decltype(it), QMultiHash<int, QString>::iterator>);
QVERIFY(it == h.end() || it.key() == 0 || it.key() == 2);
QVERIFY(it == h.end() || it.value() == "zero" || it.value() == "two");
QMultiHash<int, QString> res = {{0, "zero"), {2, "two"}};
QCOMPARE_EQ(h, res);