[Cond optimization]Behavior of annotations and xml config should keep consistent

[tswstarplanet]

I found some corresponding annotation and xml config have inconsistent behavior.
What I mean is that some required properties in xml config are not required in comparable annotation configs. For example, the interface property is required in <dubbo:service /> config. But interfaceClass or interfaceName of @service annotation is not required.
I think it is not a good design. We should make them have consistent behavior because it can make processing of config clearer and simpler.

[mercyblitz]

The related issue : apache/dubbo-spring-boot-project#382

[mercyblitz]

Fixed.