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/PosixTarHeader.java

@@ -279,9 +279,9 @@ public final class PosixTarHeader {
   @Override
   public boolean equals(@Nullable Object rhs) {
     return rhs == this
-        || rhs != null
-        && getClass() == rhs.getClass()
-        && Arrays.equals(header, ((PosixTarHeader) rhs).header);
+        || (rhs != null
+            && getClass() == rhs.getClass()
+            && Arrays.equals(header, ((PosixTarHeader) rhs).header));
   }
 
   /** @see Arrays#toString(byte[]) */