zstreamdump: add per-record-type counters and an overhead counter

Count the bytes of payload for each replication record type

Count the bytes of overhead (replication records themselves)

Include these counters in the output summary at the end of the run.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Signed-off-by: Allan Jude <allanjude@freebsd.org>
Sponsored-By: Klara Systems and Catalogic
Closes #8432