The API reduces the amount of manual plumbing required to offer a
conceptual property through the traditional setter/getter API as well as
through QProperty<T> API. Since the latter would require inlining the
type and thus making it impossible to add new properties without
breaking binary compatibility, this patch introduces a fake API that
behaves similar but does not contain the property by value.
Change-Id: Ib9bccd867f0e4e36a520e5583ba348e728284253
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>