Improving support for `CREATE PROCEDURE`

sqlparser-rs currently doesn't have great support for `CREATE PROCEDURE` statements, leading to parser errors when I pass in valid SQL. I'd like to work on improving this (I've already started on [my fork](https://github.com/ZacJW/sqlparser-rs/tree/dev)).

What's the project's ideal vision for how this would be handled? Stored procedures are the kind of thing that can be very RDBMS specific. Do you just want the AST to cover what's in the standard, but the dialects to accept but discard additional options?

The first fix which will be ready to go once I've written tests is #1901, support for what PostgreSQL calls argmode and the standard calls parameter mode.

## PRs

- #1901
- #1903

Empieza revisando el trabajo existente en la rama dev del fork del autor y las issues y PRs enlazadas #1901 y #1903. Aclara el comportamiento previsto del proyecto para AST y los dialectos con CREATE PROCEDURE y, después, añade pruebas que cubran el soporte acordado para que el SQL válido se analice como se espera.

Escrito por el modelo de indexación a partir del texto del issue.