Improve field info metadata queries.

[jheer]

• Add Query.describe(query) to generate DESCRIBE ... queries for metadata.
• Add support for arbitrary SQL expressions (not just column names) as field info metadata.
• Add support to convert Apache Arrow DECIMAL values to JavaScript Number values.
• Update query consolidator to handle DESCRIBE queries, which require filtering rather than projection.
• Remove table catalog from Coordinator, rely on cache and consolidation instead.
• Refactor fieldInfo metadata management within vgplot Mark implementations.
• Refactor Apache Arrow utilities to be exports of @uwdata/mosaic-core.

As a result of the above, the catalog option of Coordinator.clear is no longer supported. Clients can still pass the options, but it will have no effect. Instead, clearing the cache will now also drop any cached table metadata.

This PR fixes the issue raised here: observablehq/framework#1015 (comment).
Passing SQL expressions such as {x: vg.sql`-ra`} should now work.