Modify the scope_depth for variables in lambdas

[filipsajdak]

If a variable parent is a function without the name, the scope_depth is increased by 1. Refrain from being mixed with variables from the scope where lambda was created.

After this change, the following code:

f_inout: (inout x) -> _ = {
    x *= 2;
    return x;
}

main: () -> int = {
    x := 21;

    l1 := :(forward x) = {
        std::cout << f_inout(forward x) << std::endl;
    };

    l1(x);

    x++;
}

Will generate (skipping boilerplate):

[[nodiscard]] auto f_inout(auto& x) -> auto{
    x *= 2;
    return x; 
}

[[nodiscard]] auto main() -> int{
    auto x {21}; 

    auto l1 {[](auto&& x) -> void{
        std::cout << f_inout(CPP2_FORWARD(x)) << std::endl;
    }}; 

    std::move(l1)(x);

    ++x;
}

Closes #295. All regression tests pass.

[hsutter]

Thanks! Hmm. I think this will do it... I'll think some more about whether we should actually be bumping the scope depth, I wonder if there are cases for more complex nested unnamed functions where they really want their own scope level.