Add generation of batch provider

[charphi]

Having a service ...

@ServiceDefinition(quantifier = Quantifier.MULTIPLE, batch = true)
interface Rule { ... }

..., the following code ...

@ServiceProvider
enum GuidingPrinciples implements Rule { ... }

... would generate

@ServiceProvider
public final class GuidingPrinciplesRuleBatch implements RuleBatch { 
  @Override
  public Stream<Rule> getProviders() {
    return Stream.of(GuidingPrinciples.values());
  } 
}