c++: api.location.type

This feature was introduced in 95a2de5695
(which is part of 2.5), but not documented.  Give it a proper name, and
make it public.

* data/c++.m4, data/lalr1.cc, data/glr.cc, data/java.m4: Use
api.location.type instead of location_type.
* src/muscle-tab.c (muscle_percent_variable_update): Map the latter to
the former.
* tests/local.at: Adjust.
* tests/calc.at: Use api.location.type.
Leave tests/java.at with location_type, at least for the time being,
to cover both names.
* doc/bison.texi: Document api.location.type.
(User Defined Location Type): New.
* NEWS: Update.

data/glr.cc

@@ -54,7 +54,7 @@ b4_defines_if([],
               [b4_fatal([b4_skeleton[: using %%defines is mandatory]])])
 
 m4_include(b4_pkgdatadir/[c++.m4])
-b4_percent_define_ifdef([[location_type]], [],
+b4_percent_define_ifdef([[api.location.type]], [],
                         [m4_include(b4_pkgdatadir/[location.cc])])
 
 m4_define([b4_parser_class_name],
@@ -238,7 +238,7 @@ b4_copyright([Skeleton interface for Bison GLR parsers in C++],
 
 # include <string>
 # include <iostream>
-]b4_percent_define_ifdef([[location_type]], [],
+]b4_percent_define_ifdef([[api.location.type]], [],
                          [[# include "location.hh"]])[
 
 ]b4_YYDEBUG_define[
@@ -262,7 +262,7 @@ b4_user_stype
     typedef ]b4_api_PREFIX[STYPE semantic_type;
 # endif
     /// Symbol locations.
-    typedef ]b4_percent_define_get([[location_type]],
+    typedef ]b4_percent_define_get([[api.location.type]],
                                    [[location]])[ location_type;
     /// Tokens.
     struct token