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/util/XmlEnumUtils.java

@@ -21,7 +21,11 @@ public class XmlEnumUtils {
   /** Read the {@link XmlEnumValue} string off of an enum. */
   public static String enumToXml(Enum<?> input) {
     try {
-      return input.getClass().getField(input.name()).getAnnotation(XmlEnumValue.class).value();
+      return input
+          .getDeclaringClass()
+          .getField(input.name())
+          .getAnnotation(XmlEnumValue.class)
+          .value();
     } catch (NoSuchFieldException e) {
       throw new RuntimeException(e);
     }