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/ui/forms/FormFieldException.java

@@ -156,10 +156,10 @@ public final class FormFieldException extends FormException {
   @Override
   public boolean equals(@Nullable Object obj) {
     return this == obj
-        || obj instanceof FormFieldException
-        && Objects.equals(getCause(), ((FormFieldException) obj).getCause())
-        && Objects.equals(getMessage(), ((FormFieldException) obj).getMessage())
-        && Objects.equals(names, ((FormFieldException) obj).names);
+        || (obj instanceof FormFieldException
+            && Objects.equals(getCause(), ((FormFieldException) obj).getCause())
+            && Objects.equals(getMessage(), ((FormFieldException) obj).getMessage())
+            && Objects.equals(names, ((FormFieldException) obj).names));
   }
 
   @Override