Add java.nio.ByteOrder to the list of known immutable types in Wellkn…

…ownMutability.

The class is effectively an enum, although not implemented as such. It is final and does not expose any mutable fields.

Fixes #1788

PiperOrigin-RevId: 327476333

core/src/main/java/com/google/errorprone/bugpatterns/threadsafety/WellKnownMutability.java

@@ -189,6 +189,7 @@ private static ImmutableMap<String, AnnotationInfo> buildImmutableClasses(
         .add(java.math.BigInteger.class)
         .add(java.net.InetAddress.class)
         .add(java.net.URI.class)
+        .add(java.nio.ByteOrder.class)
         .add(java.nio.charset.Charset.class)
         .add(java.nio.file.Path.class)
         .add(java.nio.file.WatchEvent.class)