Make constraint based auto-complete work with alias declarations.

Feature Request

Environment

OS and Version: Ubuntu 23.04
VS Code Version: 1.79.0
C/C++ Extension Version: 1.16.3

This should be the last of my issues. I'm putting the finishing touches on my code base and this is the last of the low hanging issues with how autocomplete and intellisense work with my concept system. Really great work so far, btw. I think the autocomplete should document my library nicely.

The following is a minimal example of what I mean

template <typename Type>
concept HasFoo = requires(Type &type) {
    type.foo();
};

struct T {
    void foo () {}
};

template <HasFoo Type>
struct Foo {
    using T = Type;
    Foo () {
        T x;
        Type y;
        // T will autocomplete `foo()`, x will NOT
    }
};

int main () {
    Foo<T> a{};
}

The name T cannot be associated to anything other than Type, which will have foo() suggested for it. However this suggestion does not appear after T x.

template <typename Types>
concept HasReal = requires(typename Types::Real &real) {
    real.reduce();
};

struct T {
    struct Real {
        void reduce () {}
    };
};

template <HasReal Types>
struct Foo {
    using R = typename Types::Real x;
    Foo () {
        R x;
        typename Types::Real y;
    }
};

int main () {
    Foo<T>();
}

This is another example of the auto complete not working as expected. It will work for typename Types::Real y but not R x.

Start by reproducing the two minimal C++ examples, focusing on autocomplete and IntelliSense for concept-constrained types and alias declarations. Compare completion for the direct type declarations with the aliases; done means aliases such as T and R provide the same member suggestions as their underlying types.