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/tldconfig/idn/BUILD

@@ -11,6 +11,7 @@ java_library(
     deps = [
         "//java/google/registry/util",
         "//third_party/objectify:objectify-v4_1",
+        "@com_google_errorprone_error_prone_annotations",
         "@com_google_guava",
         "@com_google_re2j",
     ],

java/google/registry/tldconfig/idn/IdnTable.java

@@ -19,13 +19,14 @@ import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.common.collect.ImmutableRangeSet;
 import com.google.common.collect.Range;
-import com.google.common.collect.RangeSet;
+import com.google.errorprone.annotations.Immutable;
 import com.google.re2j.Matcher;
 import com.google.re2j.Pattern;
 import java.net.URI;
 import java.util.Optional;
 
 /** An IDN table for a particular TLD. */
+@Immutable
 public final class IdnTable {
 
   /** Regular expression to match a line of an IDN table. */
@@ -48,8 +49,8 @@ public final class IdnTable {
   /** Public URL of policy for this IDN table, which is needed by RDE. */
   private final URI policy;
 
-  /** {@link RangeSet} containing the valid codepoints in this table. */
-  private final RangeSet<Integer> validCodepoints;
+  /** {@link ImmutableRangeSet} containing the valid codepoints in this table. */
+  private final ImmutableRangeSet<Integer> validCodepoints;
 
   /** Validates the language rules associated with this IDN table. */
   private final Optional<LanguageValidator> languageValidator;
@@ -58,7 +59,7 @@ public final class IdnTable {
       String name,
       URI url,
       URI policy,
-      RangeSet<Integer> validCodepoints,
+      ImmutableRangeSet<Integer> validCodepoints,
       Optional<LanguageValidator> languageValidator) {
     this.name = name;
     this.url = checkNotNull(url, "%s missing '# URL: http://foo.example/page' line", name);

java/google/registry/tldconfig/idn/JapaneseLanguageValidator.java

@@ -22,12 +22,15 @@ import static java.lang.Character.UnicodeBlock.KATAKANA;
 import com.google.common.collect.ImmutableRangeSet;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Range;
+import com.google.errorprone.annotations.Immutable;
 import java.lang.Character.UnicodeBlock;
+import java.util.Objects;
 
 /**
  * Validates Japanese language domain labels. This class should only be used with a Japanese
  * language IDN table.
  */
+@Immutable
 class JapaneseLanguageValidator extends LanguageValidator {
 
   /** Any string with Japanese characters can have at most 15 characters. */
@@ -82,7 +85,8 @@ class JapaneseLanguageValidator extends LanguageValidator {
       // The KATAKANA_HIRAGANA_PROLONGED_SOUND_MARK can only occur after a HIRAGANA or KATAKANA
       // character.
       if (codepoint == KATAKANA_HIRAGANA_PROLONGED_SOUND_MARK
-          && precedingUnicodeBlock != HIRAGANA && precedingUnicodeBlock != KATAKANA) {
+          && !Objects.equals(precedingUnicodeBlock, HIRAGANA)
+          && !Objects.equals(precedingUnicodeBlock, KATAKANA)) {
         return false;
       }
 

java/google/registry/tldconfig/idn/LanguageValidator.java

@@ -15,8 +15,10 @@
 package google.registry.tldconfig.idn;
 
 import com.google.common.collect.ImmutableMap;
+import com.google.errorprone.annotations.Immutable;
 import java.util.Optional;
 
+@Immutable
 abstract class LanguageValidator {
 
   /** A registry of all known language validators keyed by their language code. */