support MariaDB 12.3 XML data type.

MariaDB 12.3 introduced a native XML column type with MDEV-37261.
Currently, Connector/J does not recognize this type and falls back to treating it as a plain String (mapped to Types.LONGVARCHAR or similar). This means ResultSetMetaData.getColumnType() does not return Types.SQLXML and ResultSet.getSQLXML() is not usable in a spec-compliant way.

Expected behavior:

ResultSetMetaData.getColumnTypeName() should return "XML" for XML columns.
ResultSetMetaData.getColumnType() should return java.sql.Types.SQLXML (type code 2009).
ResultSet.getSQLXML(int/String) should return a valid java.sql.SQLXML instance backed by the column value.
PreparedStatement.setSQLXML(int, SQLXML) should correctly bind XML values when inserting or updating XML columns.