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/model/host/HostResource.java

@@ -149,7 +149,7 @@ public class HostResource extends EppResource implements ForeignKeyedEppResource
         Optional.ofNullable(getLastSuperordinateChange()).orElse(getCreationTime());
     DateTime lastTransferOfCurrentSuperordinate =
         Optional.ofNullable(superordinateDomain.getLastTransferTime()).orElse(START_OF_TIME);
-    return (lastSuperordinateChange.isBefore(lastTransferOfCurrentSuperordinate))
+    return lastSuperordinateChange.isBefore(lastTransferOfCurrentSuperordinate)
         ? superordinateDomain.getLastTransferTime()
         : getLastTransferTime();
   }