Replace public operators operator==(), operator!=() of
QJsonValue/QJsonValueConstRef/QJsonValueRef classes to friend
methods comparesEqual().
Use QT_CORE_REMOVED_SINCE and removed_api.cpp to get rid of current
comparison methods and replace them with a friend.
Delete non-exported public operators operator==(), operator!=()
for QJsonValueConstRef/QJsonValueRef classes.
Add comparison check to auto-test.
Task-number: QTBUG-120300
Change-Id: I01434af4ce5a7589733db4a9b14f54ad42e852ed
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
839cffd521