Once more refactor arc_summary output

Before this arc_summary was not reporting any information about
evictable ARC memory. As result I've found difficult to analyze
behavior of dnode-heavy workload with lots of unevictable buffers.

This change adds evictable sizes into states breakdown section.
While there, add/refactor sections for global memory statistics,
for ARC breakdown between different structures, for data/metadata.
Add information about memory reclamation requests.

While there, refactor and polish graph mode, neglected for a while.

Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Umer Saleem <usaleem@ixsystems.com>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>