Was done in code in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/FlaggedRevs/+/369460/5/backend/schema/mysql/patch-fr_user-index.sql
Never got applied in production.
- ALTERs to run: TBD
- Where to run those changes: flaggedrevs.dblist
- When to run those changes: At any time
- If the schema change is backwards compatible: Yes.
- If the schema change has been tested already on some of the test/beta wikis: This has been around for ten years on new wikis.
- if the data should be made available on the labs replicas and/or dumps: The table only contains public data.