Replace loadByUniqueId() with methods that don't overload unique id

It is replaced by loadByForeignKey(), which does the same thing that
loadByUniqueId() did for contacts, hosts, and domains, and also
loadDomainApplication(), which loads domain application by ROID. This eliminates
the ugly mode-switching of attemping to load by other foreign key or ROID.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=133980156

javatests/google/registry/flows/domain/DomainTransferRequestFlowTest.java

@@ -147,7 +147,7 @@ public class DomainTransferRequestFlowTest
     assertTransactionalFlow(true);
     runFlowAssertResponse(readFile(expectedXmlFilename, substitutions));
     // Transfer should have been requested. Verify correct fields were set.
-    domain = reloadResourceByUniqueId();
+    domain = reloadResourceByForeignKey();
     final HistoryEntry historyEntryTransferRequest =
         getOnlyHistoryEntryOfType(domain, HistoryEntry.Type.DOMAIN_TRANSFER_REQUEST);
     int registrationYears = domain.getTransferData().getExtendedRegistrationYears();
@@ -503,7 +503,7 @@ public class DomainTransferRequestFlowTest
 
   @Test
   public void testSuccess_autorenewBeforeAutomaticTransfer() throws Exception {
-    DomainResource oldResource = persistResource(reloadResourceByUniqueId().asBuilder()
+    DomainResource oldResource = persistResource(reloadResourceByForeignKey().asBuilder()
         .setRegistrationExpirationTime(clock.nowUtc().plusDays(1).plus(1))
         .build());
     clock.advanceOneMilli();