sqlite: support sqlite3_create_function

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What is the problem this feature will solve?

With sqlite3_create_function(), it's easy to implement customized queries such as regex or nlp search. Also, this enhances alignment with existing sqlite3 libraries in Node.JS world such as sql.js or bettersqlite.

What is the feature you are proposing to solve the problem?

Expose an API like this

What alternatives have you considered?

No response