src: mark some global state as const

Mark some global variables as `const` or `constexpr`.

PR-URL: https://github.com/nodejs/node/pull/25052


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>