sql/catalog: use in-memory immutable descriptors instead of ResolvedSchema for descriptorless schemas? #57538
Description
Temporary, virtual, and (for now) public schemas don't have on-disk schema descriptors. We currently return them from the descriptor access and name resolution APIs as catalog.ResolvedSchema. Perhaps we should just put them behind an immutable schema descriptor interface instead. It may be ideal to not support mutable access.
This would have the advantage of making all the descriptor APIs consistent.
Epic: CRDB-2454
Jira issue: CRDB-3522