Better handling of error spans from schema objects

```
warning: QueryError
┌─ <895e407e-2614-11f0-8abe-7f96c9e30a51 expr>:2:45
│
2 │ __scope_0_defaultcurrentUser := (GLOBAL default::currentUser)
│ ╭─────────────────────────────────────────────^
3 │ │ SELECT __scope_0_defaultcurrentUser {
│ ╰─────────────────────────────^ possibly more than one element returned by an expression in a FILTER clause
```

Here, `<895e407e-2614-11f0-8abe-7f96c9e30a51 expr>` is indicating that the source of the error span is from the `expr` field of the schema object with id `895e407e-2614-11f0-8abe-7f96c9e30a51`, and *not* from the base query itself.

We should avoid highlighting in the query itself in that case, and *maybe* could eventually consider querying the schema to get source?

Oh, or maybe we should extend the protocol to know how to collect those sources and bundle them?