The descriptions can serve as documentation in the code,
and they can be used to provide better help.
Copy property descriptions when copying alias properties.
Cc: Markus Armbruster <firstname.lastname@example.org>
Signed-off-by: Gonglei <email@example.com>
Reviewed-by: Paolo Bonzini <firstname.lastname@example.org>
Reviewed-by: Michael S. Tsirkin <email@example.com>
Signed-off-by: Andreas Färber <firstname.lastname@example.org>