sql,ast: better redact support for statements

[ajwerner]

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

Currently the cockroach code generates an anonymized string for statements by formatting the AST to hide all constants. This ends up preserving relation names but losing information about columns making it hard to unpack the structure of a statement.

cockroach/pkg/ccl/backupccl/restore_job.go

Line 1805 in 3d920ee

updatedPrivileges = sql.CreateInheritedPrivilegesFromDBDesc(parentDB, user)

Another issue is that we pass this anonymized statement around as a string. That means that if we log it or include it in an error without remembering to wrap it in redact.Safe or log.Safe then it will be redacted. Ideally we'd be able to get nice redacted statement structure that might even be able to preserve more of the structure than we do today.

Describe the solution you'd like

I see several options with some tradeoffs. We may want to do all of them. The details are intentionally vague.

1. Implement redact.SafeMessage or something like it on all of the ast statements (or even add it to the interface). This would eliminate the need to call log.Safe but doesn't make the story around constants any better.
2. Implement some middleware SafePrinter that can remap constants to hashes as appropriate or something like that
3. Implement a more stateful SafePrinter that might have access to column identifiers and table identifiers. This might be better served as an AST transformation pre-processing step rather than as something that happens during formatting.

Epic: CRDB-6668

Jira issue: CRDB-3621

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