C++: new C++23 escape sequence, fix comments and # in "namespace identifier" and attribute

- add `\o{n...}`
- add `\x{n...}`
- add `\u{n...}`
- add `\N{name}`
- fix comments in namespace: `std::vector/*...*/<T>` / `std::chrono::/*milli*/seconds`
- fix `#` and `##` in `std::uint##n##_t`