[libc++][spaceship] Fixed `__debug_three_way_comp`'s `operator()` for `vector<bool>'s `operator<=>`

An issue with `operator()` was found during the implementation of https://reviews.llvm.org/D132268.

This patch aims to resolve the issues by updating the operator to use perfect forwarding.

The original motivation for `three_way_comp_ref_type` is given in: https://reviews.llvm.org/D131395

`three_way_comp_ref_type`'s implementation is inspired by `comp_ref_type`, which has two overloads:

```
    template <class _Tp, class _Up>
    bool operator()(const _Tp& __x,  const _Up& __y);

    template <class _Tp, class _Up>
    bool operator()(_Tp& __x,  _Up& __y);
```

`__debug_three_way_comp` is missing the first overload and also declares the typealias`_three_way_comp_ref_type ` incorrectly.

Reviewed By: #libc, philnik

Differential Revision: https://reviews.llvm.org/D150188