Package-wide TYPE for variable declarations

This tasks is a subtask of MDEV-13139.

Under terms of this task we'll implement a way to declare SP variables using TYPE declarations from package specifications.

For example:

This package specification declares a public data type varchar_array:

SET sql_mode=ORACLE;

DELIMITER $$

CREATE OR REPLACE PACKAGE pkg AS

  TYPE varchar_array IS TABLE OF VARCHAR(2000) INDEX BY INTEGER;

END;

$$

DELIMITER ;

This procedure uses the data type varchar_array using a qualified notation:

DELIMITER $$

CREATE OR REPLACE PROCEDURE p1 AS

  v pkg.varchar_array;

BEGIN

  v(0):='test';

  SELECT v(0);

END;

$$

DELIMITER ;

CALL p1();

+------+

| v(0) |

+------+

| test |

+------+

Note, this task is only about variables. Stored routine parameters and stored function return values will be implemented separately.