Allow block cloning across encrypted datasets

When two datasets share the same master encryption key, it is safe
to clone encrypted blocks. Currently only snapshots and clones
of a dataset share with it the same encryption key.

Added a test for:
- Clone from encrypted sibling to encrypted sibling with
  non encrypted parent
- Clone from encrypted parent to inherited encrypted child
- Clone from child to sibling with encrypted parent
- Clone from snapshot to the original datasets
- Clone from foreign snapshot to a foreign dataset
- Cloning from non-encrypted to encrypted datasets
- Cloning from encrypted to non-encrypted datasets

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Original-patch-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Signed-off-by: Kay Pedersen <mail@mkwg.de>
Closes #15544

tests/test-runner/bin/zts-report.py.in

@@ -305,6 +305,8 @@ elif sys.platform.startswith('linux'):
             ['SKIP', cfr_cross_reason],
         'block_cloning/block_cloning_copyfilerange_fallback_same_txg':
             ['SKIP', cfr_cross_reason],
+        'block_cloning/block_cloning_cross_enc_dataset':
+            ['SKIP', cfr_cross_reason],
     })