Materialize recursive_wrapper<T> instead of T when possible

[saki7]

Uses the functionality implemented in iris-cpp/iris#18

This PR solves the issue described in:

x4/include/iris/x4/traits/variant_traits.hpp

Lines 46 to 65 in 23686c5

	template<class Attr, class First, class... Rest>
	struct variant_find_substitute_impl<Attr, First, Rest...>
	{
	using type = std::conditional_t<
	is_substitute_v<Attr, iris::unwrap_recursive_type<First>>,
	// Given some type `T`, when both `T` and `recursive_wrapper<T>` is seen
	// during attribute resolution, X4 should ideally materialize the latter
	// because:
	// - It means that the user has supplied at least one explicit type
	// (i.e. exposed attribute type, possibly a rule attribute type) that
	// is `recursive_wrapper<T>`, and
	// - constructing `T` and then moving it to `recursive_wrapper<T>`
	// involves copying from stack to heap.
	//
	First, // no need to unwrap due to the reason described above
	typename variant_find_substitute_impl<Attr, Rest...>::type
	>;
	};