Clean up foreign key resolution

Today, Dolt foreign keys can be persisted to disk in a resolved form, or in an unresolved form. These two different formats make it difficult to work with foreign keys and lead to obscure bugs (e.g. https://github.com/dolthub/dolt/issues/7956).

A better design would be to serialize foreign key constraints identically in all cases, and always resolve them as part of analysis.