qmp: add 'get-win32-socket'

A process with enough capabilities can duplicate a socket to QEMU. Add a
QMP command to import it and add it to the monitor fd list, so it can be
later used by other commands.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230306122751.2355515-9-marcandre.lureau@redhat.com>