WL#8796 Parser refactoring and stub for role support

This worklog introduce sec. roles into the MySQL server
  + This patch implements:
    - New statement: CREATE ROLE / DROP ROLE
    - New statement: GRANT X TO Y WITH ADMIN
    - New statement: REVOKE X FROM Y
    - New statement: SET DEFAULT ROLE x
    - New statement: ALTER USER DEFAULT ROLE
    - New statement: SET ROLE
    - New system table: mysql.role_edges
    - New system table: mysql.default_roles
    - New function: role_graphml()
    - New function: current_role()
    - Extends SHOW GRANT to work with roles.
    - Introduced new error codes:
      + ER_UNKNOWN_AUTHID
      + ER_FAILED_ROLE_GRANT
      + ER_OPEN_ROLE_TABLES
      + ER_FAILED_DEFAULT_ROLES
      + ER_ROLE_NOT_GRANTED
      + ER_FAILED_REVOKE_ROLE
      + ER_RENAME_ROLE