Add object names to QGLWidget-reparenting test.

Task-number: QTBUG-31762

Change-Id: I213b4f17aa04cc99df7183df547a52c2c2a68626
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Add basic conversion functions from QVariant(QJsonValue).

There is a mismatch how QML and C++ converts QJsonValue. This patch
unifies conversions by adding QJsonValue support in QVariant::convert().

Change-Id: I8a1db3d77c517945ef48064b4b66ba03aa4f2fd0
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>