abd: lift ABD zero scan from zio_compress_data() to abd_cmp_zero()

It's now the caller's responsibility do special handling for holes if
that's something it wants.

This also makes zio_compress_data() and zio_decompress_data() properly
the inverse of each other.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Jason Lee <jasonlee@lanl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16326