libc: Move NLS catalogues to the locales packages

We don't want to put these in clibs (where libc is) since they are not
critical to system operation.  Move them to locales, since anyone who
is interested in translated versions of strerror() is going to have
that installed anyway.

While here, add some more documentation to bsd.nls.mk, particularly
the NLSPACKAGE option.

MFC after:	3 seconds
Reviewed by:	manu, kib
Sponsored by:	https://www.patreon.com/bsdivy
Differential Revision:	https://reviews.freebsd.org/D52898

lib/libc/nls/Makefile.inc

@@ -12,6 +12,11 @@ MAN+=	catclose.3 catgets.3 catopen.3
 #       for translators.
 
 NLSNAME=	libc
+# We don't want libc's NLS catalogues to be installed in the clibs package.
+# Put them in locales instead, since anyone interested in NLS will have
+# that installed.
+NLSPACKAGE=	locales
+
 NLS+=	be_BY.UTF-8
 NLS+=	ca_ES.ISO8859-1
 NLS+=	de_DE.ISO8859-1

share/mk/bsd.nls.mk

@@ -1,6 +1,8 @@
 #
-# This include file <bsd.nls.mk> handles building and installing Native
-# Language Support (NLS) catalogs
+# Handle building and installing Native Language Support (NLS) catalogs.
+# This is implemented using a <bsd.files.mk> files group called "NLS",
+# so any per-group options that bsd.files.mk supports can be used here
+# with the prefix "NLS".
 #
 # +++ variables +++
 #
@@ -17,6 +19,9 @@
 # NLSMODE	National Language Support files mode. [${NOBINMODE}]
 #
 # NLSOWN	National Language Support files owner. [${SHAREOWN}]
+#
+# NLSPACKAGE	Package to install the NLS files in.
+#		[${PACKAGE}, or "utilities" if not set]
 
 .if !target(__<bsd.init.mk>__)
 .error bsd.nls.mk cannot be included directly.