Ask IFactory for implementation before creating Proxy for interface

[remkop]

CommandReflection currently creates a java.lang.reflect.Proxy unconditionally when an interface class is passed in. It should ask the IFactory for an implementation first.

[remkop]

Dependency Injection example.

Guice-based IFactory:

import com.google.inject.*;
import picocli.CommandLine.IFactory;

public class GuiceFactory implements IFactory {
    private final Injector injector = Guice.createInjector(new DemoModule());

    @Override
    public <K> K create(Class<K> aClass) throws Exception {
        return injector.getInstance(aClass);
    }

    static class DemoModule extends AbstractModule {
        @Override
        protected void configure() {
            bind(java.util.List.class).to(java.util.LinkedList.class);
            bind(Runnable.class).to(InjectionDemo.class);
        }
    }
}

Picocli command with injected resource:

import picocli.CommandLine;
import javax.inject.Inject;

@CommandLine.Command(name = "di-demo")
public class InjectionDemo implements Runnable {
    @Inject java.util.List list;

    @CommandLine.Option(names = "-x") int x;

    public static void main(String[] args) {
        CommandLine.run(Runnable.class, new GuiceFactory(), args);
    }

    @Override
    public void run() {
        assert list instanceof java.util.LinkedList;
    }
}