Add DarkPointer factory method for unique_ptr

[thirtytwobits]

    template <typename T>
    using allocator_t = cetl::pmr::polymorphic_allocator<T>;

    template <typename T>
    using dark_ptr_t = std::unique_ptr<T, cetl::pmr::PolymorphicDeleter<allocator_t<T>>>;

    /// Construct a new concrete type but return a unique_ptr to an interface type for the concrete object.
    /// Because the concrete type is no longer visible, except by using RTTI or IPolymorphicType, after the
    /// pointer is constructed it is referred to as a "Dark" pointer.
    template <typename InterfaceType, typename ConcreteType, typename... Args>
    static dark_ptr_t<InterfaceType> make_unique(allocator_t<ConcreteType> concrete_allocator, Args&&... args)
    {
...

One of the dangers of the dark pointer is, if a user calls release the object returned cannot be safely deleted unless the caller also gets the deleter. It might be worth encapsulating std::unique_ptr to account for this danger?