"signal someSignal(var foo)" mapped to foo being of type QVariant.
Unfortunately that is a "lossy" type and it cannot represent all JavaScript
values, including for example function closures (as reported in the JIRA bug).
Instead we should use QJSValue. It is an important behavioural change because
it affects the presumably rare case of somebody declaring a signal in QML with
such a parameter and connect to it from C++ (or trying to emit it) - in that
situation the code needs to be changed.

Task-number: QTBUG-35171
Change-Id: I4fb4a18b407e4ea6c28a3a297fc6f76edb76d734
Reviewed-by: Lars Knoll <lars.knoll@digia.com>