Implement new rules for query refinement

[christopherswenson]

• aggregate:, group_by:, and calculate: are not legal when refining a multi stage query
• where: refines the first stage of the query
• Everything else refines the last stage of the query (limit:, having:, order_by:)

[christopherswenson]

I assume extend: will only be legal in one-stage queries as well, though we haven't discussed this.

[mtoy-googly-moogly]

This is done in https://github.com/malloydata/malloy/pull/1241