repl: add builtinModules

This adds an alias to `_builtinLibs` that is documented and should
as such also be accessed publicly. It does not contain any
underscored modules.

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>

PR-URL: https://github.com/nodejs/node/pull/33295


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>