Implements an adaptor from the notification signal of a Q_PROPERTY to
QBindable. The Q_PROPERTY does not need to be BINDABLE, but can still
be bound or used in a binding.
[ChangeLog][Core][Q_PROPERTY] Q_PROPERTYs without BINDABLE can be wrapped in QBindable to make them usable in bindings
Change-Id: Id0ca5444b93a371ba8720a38f3607925d393d98a
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>