Revise DiagStatus API

There are a number of lifecycle problems in this API.

ServiceRegistration is not idempotent. It would be nice if it were an AutoCloseable instance – yangtools.concepts.Registration preferrably, but we cannot quite have that now. Anyway unregister() should have a much-preferred idempotent close().

Furthermore ServiceDescriptor takes moduleServiceName which is also supplied to DiagStatusService.register(). This means that ServiceRegistration knows this name and hence could provide a newDescriptor(ServiceState) method without users passing this in.

Finally DiagStatusService.report() takes a ServiceDescriptor and a ServiceState, both of which are required.

Let us have a:

interface DiagStatus implements AutoCloseable {

   void report(ServiceState state);

   @Override
   close();
}

which replaces ServiceRegistration.