Support for stored procedure

We want to add support for stored procedures.

There is a thread about this feature on the SQLite forum: https://sqlite.org/forum/info/78a60bdeec7c1ee9, many use-cases are described there, and this is also something that meta added to their custom extension of SQLite for messenger: https://engineering.fb.com/2020/03/02/data-infrastructure/messenger/

We want to follow the syntax described in https://www.w3schools.com/sql/sql_stored_procedures.asp

Unresolved questions:

• How to handle procedures that depend on a table when that table is deleted
• How should procedures interact with UDF? i.e should we allow procs and UDF to conflict? This should be ok if procs are invoked with EXEC as seems to be the standard syntax in SQL.
• How should procedures be stored? As bytecode, plain SQL statement? Serialized AST?
• How should params be handled?

Start by reading the linked SQLite forum thread and the Messenger engineering post, then compare their stored-procedure use cases with the requested W3Schools syntax. Resolve how procedures depend on deleted tables, interact with UDFs, are stored, and accept parameters; the issue names no source files or tests, so completion requires defining the design before implementation.