Breaking change to current_retry_interval

Return nil after dispatch to Matching.

Consider an activity that's in retry backoff before attempt 2. This retry interval is 5s and the
next one, if there is another, will be 10s.

current_retry_interval:

         SCHEDULED       (dispatched to matching)                STARTED                (attempt completed/failed)
before               5s                                 10s                nil
after                5s                                 nil                nil

next_attempt_schedule_time for comparison:

         SCHEDULED       (dispatched to matching at t)           STARTED                (attempt completed/failed)
                     t                                  nil                nil

Author: dandavison

service/history/workflow/activity.go

@@ -121,16 +121,14 @@ func GetPendingActivityInfo(
 		if p.State == enumspb.PENDING_ACTIVITY_STATE_SCHEDULED {
 			scheduledTime := ai.ScheduledTime.AsTime()
 			if now.Before(scheduledTime) {
-				// in this case activity is waiting for a retry
+				// waiting for the retry to be dispatched to Matching
 				p.NextAttemptScheduleTime = ai.ScheduledTime
 				currentRetryDuration := p.NextAttemptScheduleTime.AsTime().Sub(p.LastAttemptCompleteTime.AsTime())
 				p.CurrentRetryInterval = durationpb.New(currentRetryDuration)
 			} else {
-				// in this case activity is at least scheduled
+				// retry has been dispatched to Matching
 				p.NextAttemptScheduleTime = nil
-				// we rely on the fact that ExponentialBackoffAlgorithm is deterministic, and  there's no random jitter
-				interval := backoff.ExponentialBackoffAlgorithm(ai.RetryInitialInterval, ai.RetryBackoffCoefficient, p.Attempt)
-				p.CurrentRetryInterval = durationpb.New(interval)
+				p.CurrentRetryInterval = nil
 			}
 		}
 	}