This does exactly what insert() on Qt associative containers does, but
allows to express the intent of using the STL-incompatible Qt insert()
semantics, in an STL-compatible way, instead of leaving the reader of
the code wondering what semantics are expected.
This is part of a very-long-term goal of fixing Qt associative
container's insert() behavior, in which QFlatMap, being an affected,
but private-API type, is used for proof-of-concept purposes.
Task-number: QTBUG-99651
Pick-to: 6.3 6.2
Change-Id: I69010285438259918aef659d3235180c1b5be696
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
6891e10f97