Is your feature request related to a problem? Please describe.

We ought to produce the same elements in the mixed version state as we do in the old version. That's how we'll ensure compatibility. We need to both do that and to validate that we do that.

Describe the solution you'd like

We need to find a way to ensure that the same statement and initial state result in the same exact state protobufs between the previous version and the current version. We could do this in a variety of ways, including writing "golden" protos on a per-release basis or finding a way to link old code directly.

Describe alternatives you've considered
There might be some way to do this as an integration test. I don't know that that would be better.

Jira issue: CRDB-15895