Persist transferredRegistrationExpirationTime (exDate) on TransferData

This CL adds transferredRegistrationExpirationTime as a TransferData field
persisted to Datastore.  It's only relevant for domains, and it represents the
registration expiration time resulting from the approval of the most recent
transfer request.  For pending transfers, we assume the transfer will be
server-approved, and thus in DomainTransferRequestFlow we set this field to the
existing computed value serverApproveNewExpirationTime, which is what we use
for setting up the server-approve autorenew billing event and poll message.
In DomainTransferApproveFlow we overwrite this field with the freshly computed
newExpirationTime, whereas in DomainTransferCancel/RejectFlow (and in the
implicit cancel of DomainDeleteFlow during a pending transfer) we null it out.

There are two key benefits to having this field, which are described in more
detail in b/36405140.

1) b/25084229 - it allows storage of a frozen value to back the "exDate" field
   of DomainTransferResponse, which we can use to fix various errors with how
   exDate display currently works.

2) b/36354434 - it allows DomainResource.cloneProjectedAtTime() to just directly
   set the registrationExpirationTime to this value, without computing it de
   novo, which reduces duplicated logic and ensures that the new expiration time
   matches the autorenew child objects.

This CL only starts writing the field on TransferData as persisted directly on
the DomainResource itself.  We'll then want to backfill the field for at
least pending transfers, whether expired or not (so we can do (2) above), but
I think we might as well backfill it for all pending and approved transfers
so that we also fix (1) even for historical transfers.  And then we can start
actually reading the field for both purposes.  (Note that for (1), this will
only fix synchronous transfer responses served via DomainTransferQueryFlow,
not async transfer responses served via poll messages, since these have already
been persisted with a potentially bad exDate, but I don't think it's worth a
backfill for those).

One last naming note: I chose the verbose transferredRegistrationExpirationTime
rather than the extendedRegistrationExpirationTime of DomainTransferResponse
because (as is the case in autorenew grace, or for a superuser transfer) the
new registration time isn't necessarily extended at all; it may be the same as
the pre-transfer expiration time.  Also, including "registration" helps clarify
w.r.t. pendingTransferExpirationTime which refers confusingly to the expiry of
the transfer itself, rather than the domain registration.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171858083

java/google/registry/model/transfer/TransferData.java

@@ -30,6 +30,8 @@ import google.registry.model.domain.Period.Unit;
 import google.registry.model.eppcommon.Trid;
 import google.registry.model.poll.PollMessage;
 import java.util.Set;
+import javax.annotation.Nullable;
+import org.joda.time.DateTime;
 
 /**
  * Common transfer data for {@link EppResource} types. Only applies to domains and contacts;
@@ -41,6 +43,34 @@ public class TransferData extends BaseTransferObject implements Buildable {
 
   public static final TransferData EMPTY = new TransferData();
 
+  /** The transaction id of the most recent transfer request (or null if there never was one). */
+  Trid transferRequestTrid;
+
+  /**
+   * The period to extend the registration upon completion of the transfer.
+   *
+   * <p>By default, domain transfers are for one year. This can be changed to zero by using the
+   * superuser EPP extension.
+   */
+  Period transferPeriod = Period.create(1, Unit.YEARS);
+
+  /**
+   * The registration expiration time resulting from the approval - speculative or actual - of the
+   * most recent transfer request, applicable for domains only.
+   *
+   * <p>For pending transfers, this is the expiration time that will take effect under a projected
+   * server approval. For approved transfers, this is the actual expiration time of the domain as
+   * of the moment of transfer completion. For rejected or cancelled transfers, this field will be
+   * reset to null.
+   *
+   * <p>Note that even when this field is set, it does not necessarily mean that the post-transfer
+   * domain has a new expiration time.  Superuser transfers may not include a bundled 1 year renewal
+   * at all, or even when a renewal is bundled, for a transfer during the autorenew grace period the
+   * bundled renewal simply subsumes the recent autorenewal, resulting in the same expiration time.
+   */
+  // TODO(b/36405140): backfill this field for existing domains to which it should apply.
+  DateTime transferredRegistrationExpirationTime;
+
   /**
    * The billing event and poll messages associated with a server-approved transfer.
    *
@@ -80,33 +110,7 @@ public class TransferData extends BaseTransferObject implements Buildable {
   @IgnoreSave(IfNull.class)
   Key<PollMessage.Autorenew> serverApproveAutorenewPollMessage;
 
-  /** The transaction id of the most recent transfer request (or null if there never was one). */
-  Trid transferRequestTrid;
-
-  /**
-   * The period to extend the registration upon completion of the transfer.
-   *
-   * <p>By default, domain transfers are for one year. This can be changed to zero by using the
-   * superuser EPP extension.
-   */
-  Period transferPeriod = Period.create(1, Unit.YEARS);
-
-  public ImmutableSet<Key<? extends TransferServerApproveEntity>> getServerApproveEntities() {
-    return nullToEmptyImmutableCopy(serverApproveEntities);
-  }
-
-  public Key<BillingEvent.OneTime> getServerApproveBillingEvent() {
-    return serverApproveBillingEvent;
-  }
-
-  public Key<BillingEvent.Recurring> getServerApproveAutorenewEvent() {
-    return serverApproveAutorenewEvent;
-  }
-
-  public Key<PollMessage.Autorenew> getServerApproveAutorenewPollMessage() {
-    return serverApproveAutorenewPollMessage;
-  }
-
+  @Nullable
   public Trid getTransferRequestTrid() {
     return transferRequestTrid;
   }
@@ -115,6 +119,30 @@ public class TransferData extends BaseTransferObject implements Buildable {
     return transferPeriod;
   }
 
+  @Nullable
+  public DateTime getTransferredRegistrationExpirationTime() {
+    return transferredRegistrationExpirationTime;
+  }
+
+  public ImmutableSet<Key<? extends TransferServerApproveEntity>> getServerApproveEntities() {
+    return nullToEmptyImmutableCopy(serverApproveEntities);
+  }
+
+  @Nullable
+  public Key<BillingEvent.OneTime> getServerApproveBillingEvent() {
+    return serverApproveBillingEvent;
+  }
+
+  @Nullable
+  public Key<BillingEvent.Recurring> getServerApproveAutorenewEvent() {
+    return serverApproveAutorenewEvent;
+  }
+
+  @Nullable
+  public Key<PollMessage.Autorenew> getServerApproveAutorenewPollMessage() {
+    return serverApproveAutorenewPollMessage;
+  }
+
   @Override
   public Builder asBuilder() {
     return new Builder(clone(this));
@@ -153,6 +181,22 @@ public class TransferData extends BaseTransferObject implements Buildable {
       super(instance);
     }
 
+    public Builder setTransferRequestTrid(Trid transferRequestTrid) {
+      getInstance().transferRequestTrid = transferRequestTrid;
+      return this;
+    }
+
+    public Builder setTransferPeriod(Period transferPeriod) {
+      getInstance().transferPeriod = transferPeriod;
+      return this;
+    }
+
+    public Builder setTransferredRegistrationExpirationTime(
+        DateTime transferredRegistrationExpirationTime) {
+      getInstance().transferredRegistrationExpirationTime = transferredRegistrationExpirationTime;
+      return this;
+    }
+
     public Builder setServerApproveEntities(
         ImmutableSet<Key<? extends TransferServerApproveEntity>> serverApproveEntities) {
       getInstance().serverApproveEntities = serverApproveEntities;
@@ -176,16 +220,6 @@ public class TransferData extends BaseTransferObject implements Buildable {
       getInstance().serverApproveAutorenewPollMessage = serverApproveAutorenewPollMessage;
       return this;
     }
-
-    public Builder setTransferRequestTrid(Trid transferRequestTrid) {
-      getInstance().transferRequestTrid = transferRequestTrid;
-      return this;
-    }
-
-    public Builder setTransferPeriod(Period transferPeriod) {
-      getInstance().transferPeriod = transferPeriod;
-      return this;
-    }
   }
 
   /**