c++: provide yy::parser::symbol_type::name

* data/skeletons/c++.m4 (yy::parser::basic_symbol::name): New.
* data/skeletons/lalr1.cc (yy_print_): Use it.
* doc/bison.texi: Document.
* tests/c++.at: Check.

doc/bison.texi

@@ -12154,6 +12154,8 @@ values, which is always less than @code{YYNTOKENS}.
 
 @deftypemethod {parser} {const char *} symbol_name (@code{symbol_kind_t} @var{symbol}) @code{const}
 The name of the symbol whose kind is @var{symbol}, possibly translated.
+
+Returns a @code{std::string} when @code{parse.error} is @code{verbose}.
 @end deftypemethod
 
 A custom syntax error function looks as follows.  This implementation is
@@ -12286,6 +12288,12 @@ applicable) location.
 The kind of this symbol.
 @end deftypemethod
 
+@deftypemethod {symbol_type} {const char *} name () @code{const}
+The name of the kind of this symbol.
+
+Returns a @code{std::string} when @code{parse.error} is @code{verbose}.
+@end deftypemethod
+
 @sp 1
 
 For each token kind, Bison generates named constructors as follows.