See comment on this PR. The "errInfo" field name (the error detail subobject that drivers surface to users) is redefined and hardcoded in several independent parts of the codebase with no shared owner.

write_ops::WriteError::kErrInfoFieldName exists but it isn't easily reusable from a core index library - depending on it would pull in the whole write_ops target for just one string, and the same name is also used for bulkWrite replies and logging.

Current instances:

• GeoKeyExtractionFailureInfo
• DocValidationError
• BatchedCommandResponse (this uses the common definition)

We should define errInfo once in a smaller dependency target and point the call sites above at it. This will probably involve splitting WriteError into its own small target so callers can reference it without bringing in the full write_ops parser target.