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"

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

java/google/registry/tools/CommandUtilities.java

@@ -35,7 +35,7 @@ class CommandUtilities {
     HOST(HostResource.class),
     DOMAIN(DomainBase.class);
 
-    private Class<? extends EppResource> clazz;
+    private final Class<? extends EppResource> clazz;
 
     ResourceType(Class<? extends EppResource> clazz) {
       this.clazz = clazz;