Merge DomainResource into DomainBase

This eliminates the use of Objectify polymorphism for EPP resources entirely
(yay!), which makes the Registry 3.0 database migration easier.

It is unfortunate that the naming parallelism of EppResources is lost between
ContactResource, HostResource, and DomainResource, but the actual type as far as
Datastore was concerned was DomainBase all along, and it would be a much more
substantial data migration to allow us to continue using the class name
DomainResource now that we're no longer using Objectify polymorphism. This
simply isn't worth it.

This also removes the polymorphic Datastore indexes (which will no longer
function as of this change). The non-polymorphic replacement indexes were added
in []

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=230930546

javatests/google/registry/tmch/LordnTaskUtilsTest.java

@@ -24,7 +24,7 @@ import static google.registry.testing.JUnitBackports.assertThrows;
 import static google.registry.testing.TaskQueueHelper.assertTasksEnqueued;
 
 import com.googlecode.objectify.Key;
-import google.registry.model.domain.DomainResource;
+import google.registry.model.domain.DomainBase;
 import google.registry.model.domain.launch.LaunchNotice;
 import google.registry.model.ofy.Ofy;
 import google.registry.model.registrar.Registrar.Type;
@@ -60,8 +60,8 @@ public class LordnTaskUtilsTest {
     inject.setStaticField(Ofy.class, "clock", clock);
   }
 
-  private DomainResource.Builder newDomainBuilder() {
-    return new DomainResource.Builder()
+  private DomainBase.Builder newDomainBuilder() {
+    return new DomainBase.Builder()
         .setFullyQualifiedDomainName("fleece.example")
         .setRegistrant(Key.create(persistActiveContact("jd1234")))
         .setSmdId("smdzzzz")
@@ -69,7 +69,7 @@ public class LordnTaskUtilsTest {
   }
 
   @Test
-  public void test_enqueueDomainResourceTask_sunrise() {
+  public void test_enqueueDomainBaseTask_sunrise() {
     persistDomainAndEnqueueLordn(newDomainBuilder().setRepoId("A-EXAMPLE").build());
     String expectedPayload =
         "A-EXAMPLE,fleece.example,smdzzzz,1,2010-05-01T10:11:12.000Z";
@@ -78,8 +78,8 @@ public class LordnTaskUtilsTest {
   }
 
   @Test
-  public void test_enqueueDomainResourceTask_claims() {
-    DomainResource domain =
+  public void test_enqueueDomainBaseTask_claims() {
+    DomainBase domain =
         newDomainBuilder()
             .setRepoId("11-EXAMPLE")
             .setLaunchNotice(
@@ -113,8 +113,8 @@ public class LordnTaskUtilsTest {
   }
 
   @Test
-  public void test_enqueueDomainResourceTask_throwsExceptionOnInvalidRegistrar() {
-    DomainResource domain =
+  public void test_enqueueDomainBaseTask_throwsExceptionOnInvalidRegistrar() {
+    DomainBase domain =
         newDomainBuilder()
             .setRepoId("9000-EXAMPLE")
             .setCreationClientId("nonexistentRegistrar")
@@ -127,9 +127,9 @@ public class LordnTaskUtilsTest {
   }
 
   @Test
-  public void test_enqueueDomainResourceTask_throwsNpeOnNullDomain() {
+  public void test_enqueueDomainBaseTask_throwsNpeOnNullDomain() {
     assertThrows(
         NullPointerException.class,
-        () -> ofy().transactNew(() -> LordnTaskUtils.enqueueDomainResourceTask(null)));
+        () -> ofy().transactNew(() -> LordnTaskUtils.enqueueDomainBaseTask(null)));
   }
 }