zdb: rework dedup accounting for log, quota and prune

The simplest thing first: add the FDT and log objects to the list of
objects to be considered when checking for leaks.

The rest is based on a conceptual change in all of this patch stack: a
block on disk with a 'D' bit is not necessarily in the DDT at all
(pruned), or in the DDT ZAPs (still on the log).

As such, walking the DDT up front is difficult (for all the reasons that
walking an unflushed log is difficult) and not really useful, since it's
not a reflection of what's on disk anyway.

Instead, we rework things here to be more like the BRT checks. When we
see a dedup'd block, we look it up in the DDT, consume a refcount, and
for the second-or-later instances, count them as duplicates.

Co-authored-by: Allan Jude <allan@klarasystems.com>
Co-authored-by: Don Brady <don.brady@klarasystems.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: iXsystems, Inc.

module/zfs/ddt.c

@@ -789,6 +789,9 @@ ddt_phys_dva_count(const ddt_univ_phys_t *ddp, ddt_phys_variant_t v,
 ddt_phys_variant_t
 ddt_phys_select(const ddt_t *ddt, const ddt_entry_t *dde, const blkptr_t *bp)
 {
+	if (dde == NULL)
+		return (DDT_PHYS_NONE);
+
 	const ddt_univ_phys_t *ddp = dde->dde_phys;
 
 	if (ddt->ddt_flags & DDT_FLAG_FLAT) {