Use fopencookie() to attach the popen fd and shell pid to the returned FILE stream instead of copying FILE into the popen container.
Keep the upstream dpopen()/dpclose() implementation as the process and descriptor backend, and make pclose() close the cookie-backed stream directly.
Fixes#2937.
Signed-off-by: Nightt <87569709+nightt5879@users.noreply.github.com>
