pathconf.2: Document the new _PC_CASE_INSENSITIVE name

Commit d6864221d8 added support for the _PC_CASE_INSENSITIVE
name for pathconf, to indicate if case insensitive lookups
are configured.

This patch documents this new name and also updates
the description for _PC_HAS_HIDDENSYSTEM to also
include UF_ARCHIVE.

This is a content change.

Reviewed by:	kib
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D53508

lib/libsys/pathconf.2

@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd August 6, 2025
+.Dd October 31, 2025
 .Dt PATHCONF 2
 .Os
 .Sh NAME
@@ -180,7 +180,8 @@ Return 1 if named attributes are enabled for the file system, otherwise 0.
 .It Li _PC_HAS_NAMEDATTR
 Return 1 if one or more named attributes exist for the file, otherwise 0.
 .It Li _PC_HAS_HIDDENSYSTEM
-Return 1 if both
+Return 1 if all of the
+.Dv UF_ARCHIVE ,
 .Dv UF_HIDDEN
 and
 .Dv UF_SYSTEM
@@ -192,6 +193,9 @@ Returns the block size required for block cloning via
 .Xr copy_file_range 2
 for a file system if block cloning is supported,
 otherwise 0.
+.It Li _PC_CASE_INSENSITIVE
+Return 1 if the file system performs case insensitive lookups,
+otherwise 0.
 .El
 .Sh RETURN VALUES
 If the call to