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

javatests/google/registry/testing/FakeServletInputStream.java

@@ -49,6 +49,11 @@ public final class FakeServletInputStream extends ServletInputStream {
     return input.read();
   }
 
+  @Override
+  public int read(byte[] b, int off, int len) throws IOException {
+    return input.read(b, off, len);
+  }
+
   @Override
   public void close() throws IOException {
     input.close();