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

先檢視作者 fork 的 dev 分支中現有的工作，以及連結的 issue 和 PR #1901、#1903。釐清專案對 CREATE PROCEDURE 的 AST 與方言行為的預期，然後新增涵蓋已達成共識之支援的測試，讓有效的 SQL 能如預期解析。

由索引模型根據 Issue 內容生成。