fs: return first folder made by mkdir recursive

mkdir('/foo/bar', { recursive: true }) and mkdirSync will now return
the path of the first folder created. This matches more closely
mkdirp's behavior, and is useful for setting folder permissions.

PR-URL: https://github.com/nodejs/node/pull/31530
Refs: https://github.com/nodejs/node/issues/31481


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>