Review request for JDK-8142422: Smaller Dynalink API adjustments

[Attila Szegedi]

Please review JDK-8142422 "Smaller Dynalink API adjustments" at <http://cr.openjdk.java.net/~attila/8142422/webrev.jdk9> for <https://bugs.openjdk.java.net/browse/JDK-8142422>

This is a potpourri of very small changes:

- made CompositeOperation, NamedOperation, and TypeUtilities final 
- DynamicLinkerFactory.DEFAULT_UNSTABLE_RELINK_THRESHOLD was made private; it needn’t be exposed
- BeansLinker static discovery methods (getReadableInstancePropertyNames and friends) return Set instead of Collection
- CompositeGuardingDynamicLinker and CompositeTypeBasedGuardingDynamicLinker are no longer Serializable (they should never have been, really).
- added documentation to private StaticClass.clazz field and readResolve() method as their documentation is used in the "Serialized Form" JavaDoc page. 
- AbstractJavaLinker.getConstructorMethod is now abstract method, and a default implementation returning null was added to BeanLinker.

Thanks,
  Attila.