[libc++][ranges] use `static operator()` for C++23 ranges (#86052)

## Abstract

This pull request converts the `operator()` of all CPOs and niebloids
related to C++23 ranges to `static`.

## Motivation

In `libc++`, CPOs and niebloids are implemented as function objects.
Currently, the `operator()` for such a function object is a
`const`-qualified member function. This means that even if the function
object is has no data members, an extra register is used to pass in the
`this` pointer when calling `operator()`, unless the compiler can inline
the function call. Declaraing `operator()` as `static` would optimize
away the unnecessary `this` pointer passing for stateless function
objects, since there is no object instance state that needs to be
accessed.

## Reference

- [P1169R4: static `operator()`](https://wg21.link/P1169R4)