sql: add descriptors.json and schema_changes.txt to stmtbundle

[virajchogle]

When investigating optimizer surprises, the bundle reviewer often needs to rule out schema-state interactions. Two new files help: descriptors.json with the pretty-printed JSON for each descriptor used by the statement, and schema_changes.txt with the recent schema-change job history for those descriptors.

The declarative schema changer drains payload.DescriptorIDs as targets complete, so completed declarative jobs have an empty descriptorIds field. PrintSchemaChanges therefore also matches the descriptor's fully-qualified name against the job's description text.

Verified manually on a single-node demo cluster:

• ALTER TABLE ... ADD COLUMN and CREATE INDEX (declarative schema changer) both appear in schema_changes.txt with status, timestamp, and description.
• descriptors.json shows the table descriptor with the new column and secondary index.
• EXPLAIN ANALYZE (DEBUG, REDACT) replaces both files with the omitted-in-redacted-bundle placeholder and does not emit errors.txt.
• EXPLAIN ANALYZE (DEBUG) SELECT count(*) FROM pg_catalog.pg_class produces clean empty-state placeholders (no errors.txt).

Fixes: #170491
Epic: None
Release note (general change): Statement bundles produced by EXPLAIN ANALYZE (DEBUG) now include descriptors.json (pretty-printed descriptor JSON for each object used by the statement) and schema_changes.txt (recent schema-change history for those descriptors).

@michae2

[trunk-io]

😎 Merged successfully - details.

[blathers-crl]

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I have added a few people who may be able to assist in reviewing:

• @michae2 (author of stmtbundle: add recent schema changes and descriptor JSON #170491)

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[cockroach-teamcity]

This change is 

[virajchogle]

Quick ping for review whenever you get a chance, happy to address any feedback.

[blathers-crl]

Thank you for updating your pull request.

My owl senses detect your PR is good for review. Please keep an eye out for any test failures in CI.

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[virajchogle]

Pushed a follow-up. The unit_tests failure was TestDistributedQueryErrorIsRetriedLocally (pkg/sql/distsql_running_test.go), which asserts on the bundle's file list. I missed updating that hardcoded list to include the two new files this PR adds (descriptors.json and schema_changes.txt). Verified the fix locally with ./dev test pkg/sql -f TestDistributedQueryErrorIsRetriedLocally now. Should be good.

[michae2]

Nice work, @virajchogle!

/trunk merge

@michae2 reviewed 3 files and all commit messages, and made 1 comment.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on virajchogle).

[blathers-crl]

Detected infrastructure failure on trunk-merge branch (matched: self-hosted runner lost communication with the server). Automatically resubmitting to merge queue (attempt 1 of 2). (run link)

[blathers-crl]

/trunk merge

[virajchogle]

Thanks for the review, @michae2! Glad to have my first CRDB PR land. More incoming!