QCborValue: fix memleak on Array to Map coercion

When converting from an array to a map, we double the number of
elements, spread the old elements out to make one free slot of space
in front of each, and then place Integer values counting from 0 into
the free slots.

The old code contained a loop that would add a strong reference to the
original elements that happen to be containers and thus are
ref-counted in the first place. But this additional strong reference
is not needed: In both cases, detached or in-place, the detach() call
that ensured unique ownership of 'map/dst' will have either directly
or indirectly updated the ref-counts of the elements correctly, and
the following loops just reshuffle the elements in the QList, they
don't create new copies (QtCbor::Elements doesn't by itself manipulate
container->ref, but even if it did, the copy would have increased, and
the assignment of the Integers would have decreased, the ref-count
again). Adding the strong ref without a user then caused the container
members to be leaked.

Fix by removing the loop.

[ChangeLog][QtCore][QCborValue] Fixed a memory leak when an array was
coerced into a map.

Amends ccea34464075759424e61806c7bc98ee3e658670.

Not picking to 6.4 as it's closed at this time.

Fixes: QTBUG-115249
Change-Id: I369c372e91c3f0cfe3c65f9b0ea8507d08fdaf48
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit ecab68989e623737f7f930d7b123471ccffbfb95)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/serialization/qcborvalue.cpp

@@ -2248,12 +2248,6 @@ static void convertArrayToMap(QCborContainerPrivate *&array)
     for (qsizetype i = 0; i < size; ++i)
         dst[i * 2] = { i, QCborValue::Integer };
 
-    // only do this last portion if we're not modifying in-place
-    for (qsizetype i = 0; src != dst && i < size; ++i) {
-        if (dst[i * 2 + 1].flags & QtCbor::Element::IsContainer)
-            dst[i * 2 + 1].container->ref.ref();
-    }
-
     // update reference counts
     assignContainer(array, map);
 }