Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

libprocstat: fix ZFS support

First of all, znode_phys_t hasn't been used for storing file attributes
for a long time now. Modern ZFS versions use a System Attribute table
with a flexible layout. But more importantly all the required
information is available in znode_t itself.

It's not easy to include zfs_znode.h in userland without breaking code
because the most interesting parts of the header are kernel-only. And
hardcoding field offsets is too fragile. So, I created a new
compilation unit that includes zfs_znode.h using some mild kludges to
get it and its dependencies to compile in userland. The compilation
unit exports interesting field offsets and does not have any other code.

PR: 194117
Reviewed by: markj
MFC after: 2 weeks
Sponsored by: Panzura
Differential Revision: https://reviews.freebsd.org/D24941