ZTS: Test for clone, mmap and write for block cloning

For block cloning, if we mmap the cloned file and write from the
map into the file, it triggers a panic in dbuf_redirty() on Linux.

The same scenario causes data corruption on FreeBSD. Both these
issues are fixed under PR#15656 and PR#15665.

It would be good to add a test for this scenario in ZTS. The test
program and issue was produced by @robn.

Reviewed-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
Closes #15717

tests/zfs-tests/cmd/.gitignore

@@ -2,6 +2,7 @@
 /btree_test
 /chg_usr_exec
 /clonefile
+/clone_mmap_write
 /devname2devid
 /dir_rd_update
 /draid