sql: include random descriptor states in randomized testing

In #79613 and #96924 we observed optimizer internal errors during unexpected descriptor states. (In the first case we made the descriptor state invalid, in the second case we will have to fix the optimizer error.)

To catch more cases like this, we should add some random descriptor states to our randomized SQL testing. (Maybe this means adding random ALTERs to sqlsmith, TLP, costfuzz, and unoptimized-query-oracle, or maybe this means creating an entirely new test. Not sure. Whatever we do, we'll need the descriptors to be in unusual states while simultaneously executing DML statements, so a serially-executed ALTER statement that completes before other statements execute might not work.)

Jira issue: CRDB-24571

Epic CRDB-30352