jobfrontier: add GetResolvedSpans/GetAllResolvedSpans

[andyyang890]

The following convenience methods would be nice:

• GetResolvedSpans(ctx context.Context, txn isql.Txn, jobID jobspb.JobID, name string) (jobspb.ResolvedSpans, bool, error): like Get, except it returns the actual resolved spans so that callers have the flexibility for whether they want to immediately put them in a frontier

• GetAllResolvedSpans(ctx context.Context, txn isql.Txn, jobID jobspb.JobID) (jobspb.ResolvedSpans, bool, error): like GetResolvedSpans, except it returns the resolved spans for all frontiers for a job, which is useful for jobs that persist multiple frontiers (e.g. CDC per-table frontiers)

  • (alternative signature) GetAllResolvedSpans(ctx context.Context, txn isql.Txn, jobID jobspb.JobID) (map[string]jobspb.ResolvedSpans, bool, error): returns a map from name to resolved spans for a job

Jira issue: CRDB-54177

[blathers-crl]

cc @cockroachdb/cdc