community(query_constructor): add mql_to_structured helper

[ianchi]

Adds a helper function to transform a mql-like dict into a FilterDirective (and be later used with any translator integration).

This can be helpful in many ways:

• to construct the FilterDirective in code from a much less verbose mql dict.
• It can also reuse mql expressions that come from other sources, as mql is a popular standard
• one source can also be from an llm as structured output directly as mql (as it is a well known format for many llm's)

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Name	Status	Preview	Comments	Updated (UTC)
langchain	⬜️ Ignored (Inspect)	Visit Preview		Feb 11, 2025 3:42am

[ccurme]

Should this live in the langchain-mongodb package?

[ianchi]

I'm not sure, but would argue that it should not.
This is more about taking advantage of a well known way of expressing a filter expression as a json.

We are using this json format even if we don't use MongoDB at all (but SQL in fact).