ANSII `character string types`

[AugustoFKL]

Implementation of all types inside the ANSII specification (1), not including the large types for now because even if they conceptually are in the same group, the implementation would be slightly different, so it's better to break the implementation.

I'll leave the length optional for all since PostgreSQL accepts them without a specific length (2).

[1] : https://jakewheat.github.io/sql-overview/sql-2016-foundation-grammar.html#character-string-type
[2] : https://www.postgresql.org/docs/current/datatype-character.html
MySQL string types: https://dev.mysql.com/doc/refman/8.0/en/char.html