test: add wasi readdir() test

This commit provides coverage for __wasi_fd_readdir().

PR-URL: https://github.com/nodejs/node/pull/35202


Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>