inspector: mark as stable

The module has been there for a while,
evidence of usage in the field exists,
and we have good test coverage for it.
Last API change has been 18 months ago.

Refs: https://github.com/nodejs/node/issues/37440#issuecomment-785763306

PR-URL: https://github.com/nodejs/node/pull/37748


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>