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/registrar/Registrar.java

@@ -130,8 +130,10 @@ public class Registrar extends ImmutableObject implements Buildable, Jsonifiable
     /**
      * Predicate for validating IANA IDs for this type of registrar.
      *
-     * @see <a href="http://www.iana.org/assignments/registrar-ids/registrar-ids.txt">Registrar IDs</a>
+     * @see <a href="http://www.iana.org/assignments/registrar-ids/registrar-ids.txt">Registrar
+     *     IDs</a>
      */
+    @SuppressWarnings("ImmutableEnumChecker")
     private final Predicate<Long> ianaIdValidator;
 
     Type(Predicate<Long> ianaIdValidator) {