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/keyring/kms/KmsConnectionImpl.java

@@ -47,11 +47,11 @@ class KmsConnectionImpl implements KmsConnection {
   @Inject
   KmsConnectionImpl(
       @Config("cloudKmsProjectId") String projectId,
-      @Config("cloudKmsKeyRing") String kmsKeyringName,
+      @Config("cloudKmsKeyRing") String kmsKeyRingName,
       Retrier retrier,
       CloudKMS kms) {
     this.projectId = projectId;
-    this.kmsKeyRingName = kmsKeyringName;
+    this.kmsKeyRingName = kmsKeyRingName;
     this.retrier = retrier;
     this.kms = kms;
   }