opt: extend opt-tester framework to mock more non-public schema objects

We currently have a way to mark columns in optimizer tests as mutation columns using a special suffix to the column name. This allows us to test invariants required of the optimizer by the schema changer (e.g. don't read from mutation columns) more directly than validating index contents after randomized tests. We should add support for non-public states in other types of schema elements, like indexes. This might have allowed us to more directly test the effect of column pruning rules that lead to https://github.com/cockroachdb/cockroach/issues/166122, and should give us a convenient way to write tests for other invariants once we make them explicit.

Jira issue: CRDB-63290