Add createtxg sort support for simple snapshot iterator

• When iterating snapshots with name only, e.g., "-o name -s name",

libzfs uses simple snapshot iterator and results are displayed
in alphabetic order. This PR adds support for faster version of
createtxg sort by avoiding nvlist parsing for properties. Flags
"-o name -s createtxg" will enable createtxg sort while using
simple snapshot iterator.

• Added support to read createtxg property directly from zfs handle

for filesystem, volume and snapshot types instead of parsing nvlist.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #13577