[lworld] Add java.util.Objects.isIdentityObject

A method is needed to identity identity object instances.
Using `o.getClass().isIdentity` is insufficient in the case of java.lang.Object.
Object.class is a special case that is neither a identity class or a value class.
But an instance of java.lang.Object is an identity object.

Adding a final instance method to Object is convenient but pollutes the method name space of all classes and may be a compatibility issue for some class somewhere.

A static `Object.isIdentityObject(o)` method would not raise compatibility issues but is not the most natural to supply the result.

`java.lang.System.isIdentityObject(o)` was also suggested. System.identityHashCode is there too.