Record if a metatype is a smart pointer to a QObject derived.

Record if a metatype is a smart pointer to a QObject derived.

This allows QVariant/QMetaType software (such as QtDeclarative) to
deal with smart pointers in a similar way to how they can deal with
naked pointers (accessing properties etc).

This also adds a requirement that T be fully defined when
QSharedPointer<T> is inserted into a QVariant.

Change-Id: I29e12b8a6aa5f4aadbd62f92b89bc238f64b5725
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@nokia.com>