zfs_znode: lift common code to a single shared file

For now, userspace has no znode implementation. Some of the property and
path handling code is used there though and is the same on all
platforms, so we only need a single copy of it.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Sponsored-by: https://despairlabs.com/sponsor/
Closes #16492

include/sys/zfs_znode.h

@@ -158,6 +158,8 @@ extern "C" {
 #define	ZFS_DIRENT_OBJ(de) BF64_GET(de, 0, 48)
 
 extern int zfs_obj_to_path(objset_t *osp, uint64_t obj, char *buf, int len);
+extern int zfs_obj_to_pobj(objset_t *osp, sa_handle_t *hdl,
+    sa_attr_type_t *sa_table, uint64_t *pobjp, int *is_xattrdir);
 extern int zfs_get_zplprop(objset_t *os, zfs_prop_t prop, uint64_t *value);
 
 #ifdef _KERNEL