QSet and std::(unordered_)set were so far not treated as appendable, as
they lack a push_back method. We do however need support for this in
declarative to enable converting back from QJSValue arrays to sets.
We achieve this by testing for and using the insert method. While vector
has also such a method, it doesn't take a single value, but rather a
position or iterator + value, so the template specialization is not
ambiguous.
Task-number: QTBUG-82743
Change-Id: I74fc7b1b856d9bcd38100b274ba2b69578ea8bbb
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
6db55e3451