memory: do_dump_memory_diagnostics(): add used and spans column to large spans section
memory: do_dump_memory_diagnostics(): add used and spans column to large spans section

Containing the amount of used memory and the amount of spans the total
memory is made up of.

cloudius-systems/seastar,syuu1228/seastar,dreamsxin/seastar,avikivity/seastar,dreamsxin/seastar,cloudius-systems/seastar,cloudius-systems/seastar,scylladb/seastar,scylladb/seastar,avikivity/seastar,dreamsxin/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar