stream: mark compose as experimental

PR-URL: https://github.com/nodejs/node/pull/39494


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>