FreeBSD: Fix the build on FreeBSD 12

It was broken for several reasons:
* VOP_UNLOCK lost an argument in 13.0.  So OpenZFS should be using
  VOP_UNLOCK1, but a few direct calls to VOP_UNLOCK snuck in.
* The location of the zlib header moved in 13.0 and 12.1.  We can drop
  support for building on 12.0, which is EoL.
* knlist_init lost an argument in 13.0.  OpenZFS change 9d0887402b
  assumed 13.0 or later.
* FreeBSD 13.0 added copy_file_range, and OpenZFS change 67a1b03791
  assumed 13.0 or later.

Sponsored-by: Axcient
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Alan Somers <asomers@gmail.com>
Closes #15551

include/os/freebsd/spl/sys/vnode.h

@@ -56,6 +56,7 @@ enum symfollow { NO_FOLLOW = NOFOLLOW };
 #ifndef IN_BASE
 #include_next <sys/vnode.h>
 #endif
+#include <sys/ccompat.h>
 #include <sys/mount.h>
 #include <sys/cred.h>
 #include <sys/fcntl.h>
@@ -104,7 +105,7 @@ vn_flush_cached_data(vnode_t *vp, boolean_t sync)
 		zfs_vmobject_wlock(vp->v_object);
 		vm_object_page_clean(vp->v_object, 0, 0, flags);
 		zfs_vmobject_wunlock(vp->v_object);
-		VOP_UNLOCK(vp);
+		VOP_UNLOCK1(vp);
 	}
 }
 #endif