In addition (and as a fallback) from requiring qHash, add support
for std::hash specializations. This catches two birds with one stone:
1) users of Qt can simply specialize std::hash for their datatypes,
and use them in both QHash and stdlib unordered associative containers;
2) we get QHash support for any (stdlib) datatype that is hashable
without having to overload qHash for them.
[ChangeLog][QtCore][QHash] QHash, QMultiHash and QSet now support
for key types anything that can be hashed via std::hash, instead of
always requiring a qHash() overload.
Change-Id: Ib5ecba86e4b376d318389500bd24883ac6534c5f
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
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