Add sql_mode specific tokens for keywords BLOB, CLOB, NUMBER, RAW, VARCHAR2

Keywords BLOB, CLOB, NUMBER, RAW, VARCHAR2 appear in different context in sql_yacc.yy and sql_yacc_ora.yy.

To unify sql_yacc.yy and sql_yacc_ora.yy easier, we'll add sql_mode specific tokens for these keywords and modify the grammar in sql_yacc.yy and sql_yacc_ora.yy accordingly.

Instead of say BLOB_SYM, we'll have separate BLOB_MARIADB_SYM and BLOB_ORACLE_SYM.

This will make possible for native and Oracle grammar rules to co-exists in the same *.yy file.

By default, Lex_input_stream::find_keyword() will return XXX_MARIADB_SYM, and translate it to XXX_ORACLE_SYM in Oracle compatibility mode:

    if (m_thd->variables.sql_mode & MODE_ORACLE)

    {

      switch (symbol->tok) {

        ...

        case BLOB_MARIADB_SYM:         return BLOB_ORACLE_SYM;

        ...

      }

    }