refactor: remove v2 types

[hallettj]

Removes v2 types, and replaces them with a new set of internal types that closely match ndc models. The root of the new types is called QueryPlan instead of QueryRequest. It is a denormalized version of a query request. In particular QuerPlan

• puts type annotations on fields, variable references, etc.
• uses a Type type that inlines object type references
• collects relationship reference details from all fields, filters, and sorts and places relevant details in one map in each sub-query (instead of having one relations map at the QueryRequest level, the new types have a map on each Query value for relations with that query's collection as a source, and that are referenced in that query)
• collects one map of join details at the QueryPlan level (the analog of QueryRequest) for existence checks on unrelated collections

The changes simplify emitting MongoDB aggregation code, and lower the impedence mismatch to using features of v3 that aren't reflected in v2.

I preserved and updated all the existing tests except one that tests filtering by fields of a nested object of a related collection which is something that worked in v2, but will require an update to the latest ndc-spec to work in v3.

There are some more changes necessary for filtering and sorting by fields of a related collection. We need to adjust the way query request expressions map to MongoDB expressions. I thought it would be best to get this refactor in, and put those changes in a separate PR.

[dmoverton]

Looks good. This is a big improvement. Just a few minor suggested changes.

It might be useful to move the ndc-query-plan crate to the SDK at some point so it can be used by other connectors.

[hallettj]

Looks good. This is a big improvement. Just a few minor suggested changes.

It might be useful to move the ndc-query-plan crate to the SDK at some point so it can be used by other connectors.

Thanks! I had the same thought.