Fix various Error Prone errors that were found by the FOSS build

Most common:
- Unnecessary parentheses and operator precedence clarify (self-explanatory)
- Reference equality--there were a few instances of using == or != improperly
- Qualification of Builder (and similar) imports so that it's clear which type of Builder we're referring to
- Marking some immutable classes with @Immutable since EP desires that all enums be deeply immutable
- String.split() having "surprising behavior"

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=230971531

java/google/registry/rde/ContactResourceToXjcConverter.java

@@ -36,6 +36,7 @@ import google.registry.xjc.eppcom.XjcEppcomTrStatusType;
 import google.registry.xjc.rdecontact.XjcRdeContact;
 import google.registry.xjc.rdecontact.XjcRdeContactElement;
 import google.registry.xjc.rdecontact.XjcRdeContactTransferDataType;
+import java.util.Objects;
 import javax.annotation.CheckForNull;
 import javax.annotation.Nullable;
 
@@ -101,7 +102,7 @@ final class ContactResourceToXjcConverter {
     //       required before an automated response action will be taken by
     //       the registry.  For all other status types, the value identifies
     //       the date and time when the request was completed.
-    if (model.getTransferData() != TransferData.EMPTY) {
+    if (!Objects.equals(model.getTransferData(), TransferData.EMPTY)) {
       bean.setTrnData(convertTransferData(model.getTransferData()));
     }