allocator: move isDecommissionAction to allocatorimpl

This commit refactors isDecommissionAction into allocatorimpl for consistency
with other similar helpers like allocatorActions.{Add,Replace,Remove}. This
change has no behavior changes but to make future commits easier.

Author: wenyihu6

pkg/kv/kvserver/allocator/allocatorimpl/allocator.go

@@ -163,6 +163,15 @@ func (a AllocatorAction) Remove() bool {
 		a == AllocatorRemoveDecommissioningNonVoter
 }
 
+// Decommissioning indicates an action replacing or removing a decommissioning
+// replicas.
+func (a AllocatorAction) Decommissioning() bool {
+	return a == AllocatorRemoveDecommissioningVoter ||
+		a == AllocatorRemoveDecommissioningNonVoter ||
+		a == AllocatorReplaceDecommissioningVoter ||
+		a == AllocatorReplaceDecommissioningNonVoter
+}
+
 // TargetReplicaType returns that the action is for a voter or non-voter replica.
 func (a AllocatorAction) TargetReplicaType() TargetReplicaType {
 	var t TargetReplicaType

pkg/kv/kvserver/replicate_queue.go

@@ -923,19 +923,12 @@ func (rq *replicateQueue) processOneChange(
 }
 
 func maybeAnnotateDecommissionErr(err error, action allocatorimpl.AllocatorAction) error {
-	if err != nil && isDecommissionAction(action) {
+	if err != nil && action.Decommissioning() {
 		err = decommissionPurgatoryError{err}
 	}
 	return err
 }
 
-func isDecommissionAction(action allocatorimpl.AllocatorAction) bool {
-	return action == allocatorimpl.AllocatorRemoveDecommissioningVoter ||
-		action == allocatorimpl.AllocatorRemoveDecommissioningNonVoter ||
-		action == allocatorimpl.AllocatorReplaceDecommissioningVoter ||
-		action == allocatorimpl.AllocatorReplaceDecommissioningNonVoter
-}
-
 // shedLease takes in a leaseholder replica, looks for a target for transferring
 // the lease and, if a suitable target is found (e.g. alive, not draining),
 // transfers the lease away.