The refactoring to use CBOR missed two places where we could assign from
the same object and thus cause corruption. In fixing this issue, I found
a design flaw in QJsonObject, see Q_EXPECT_FAILing unit test and task
QTBUG-83398.
[ChangeLog][QtCore][QJsonObject] Fixed a regression from 5.13 that
incorrect results when assigning elements from an object to itself.
Fixes: QTBUG-83366
Change-Id: Ibdc95e9af7bd456a94ecfffd1603df24b06713aa
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
ddc7b3c156