More constructors and member functions for `vk::raii::PluralType`

[sharadhr]

From #2413:

It would be nice to implement an operator*() or ::value() member function for vk::raii::PluralType that returns a std::vector<vk::SingularType> (note: no ::raii); this would recursively call operator*().

And similarly to construct the plural types from an ArrayProxy<vk::SingularType>&& (note temporary so that the resultant container takes ownership of the arguments), and also note again no ::raii). This would facilitate interoperation with other libraries.