Let's say that if "givenname" is empty, "sn" is the full name

Maybe eventually we can get rid of attempts in LibreOffice to
interpret names as consisting of culture-dependent parts like "given
name", "father's name", "last name" etc and just treat names as opaque
strings. Let's start by saying explicitly that if "givenname" is empty
but "sn" is not, then "sn" is the full name.

See https://www.kalzumeus.com/2010/06/17/falsehoods-programmers-believe-about-names/

Change-Id: Id2c1df08c8faf65fd25d46a4380f5f53e60d5378

officecfg/registry/schema/org/openoffice/UserProfile.xcs

@@ -51,7 +51,13 @@
         <!-- OldLocation: soffice.ini -->
         <!-- UIHints: Tools - Options - General - User Data -->
         <info>
-          <desc>Specifies the last name of the user.</desc>
+          <desc>If givenname is empty, specifies the name of the user,
+          in the preferred form the user wants it to be displayed,
+          intentionally without any hints how to split it into "given"
+          name, "family name", "patronym", "middle initial" and other
+          similar culture-dependent components of a person's name. If
+          givenname is non-empty, this is supposed to be the "last
+          name".</desc>
         </info>
         <value/>
         <!-- JB: Empty default inserted into empty property node. Remove if NIL was intended -->