Add methods make() and append_uniq() to Row_definition_list

row_field_name:

          ident // or ident_directly_assignable

          {

            if (unlikely(check_string_char_length(&$1, 0, NAME_CHAR_LEN,

                                                  system_charset_info, 1)))

              my_yyabort_error((ER_TOO_LONG_IDENT, MYF(0), $1.str));

            if (unlikely(!($$= new (thd->mem_root) Spvar_definition())))

              MYSQL_YYABORT;

            Lex->init_last_field($$, &$1, thd->variables.collation_database);

          }

        ;

row_field_definition_list:

          row_field_definition

          {

            if (unlikely(!($$= new (thd->mem_root) Row_definition_list())) ||

                unlikely($$->push_back($1, thd->mem_root)))

              MYSQL_YYABORT;

          }

        | row_field_definition_list ',' row_field_definition

          {

            uint unused;

            if (unlikely($1->find_row_field_by_name(&$3->field_name, &unused)))

              my_yyabort_error((ER_DUP_FIELDNAME, MYF(0), $3->field_name.str));

            $$= $1;

            if (unlikely($$->push_back($3, thd->mem_root)))

              MYSQL_YYABORT;

          }

        ;

row_field_name:

          ident  // or ident_directly_assignable

          {

            if (!($$= Lex->row_field_name(thd, $1)))

              MYSQL_YYABORT;

          }

        ;

row_field_definition_list:

          row_field_definition

          {

            if (!($$= Row_definition_list::make(thd->mem_root, $1)))

              MYSQL_YYABORT;

          }

        | row_field_definition_list ',' row_field_definition

          {

            if (($$= $1)->append_uniq(thd->mem_root, $3))

              MYSQL_YYABORT;

          }

        ;