ServiceDescriptor (Apache Dubbo 2.7.18 API)

```
public class ServiceDescriptor
extends Object
```
ServiceModel and ServiceMetadata are to some extend duplicated with each other. We should merge them in the future.

Constructors
Constructor and Description
`ServiceDescriptor(Class<?> interfaceClass)`

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`Set<MethodDescriptor>`	`getAllMethods()`
`MethodDescriptor`	`getMethod(String methodName, Class<?>[] paramTypes)` Does not use Optional as return type to avoid potential performance decrease.
`MethodDescriptor`	`getMethod(String methodName, String params)` Does not use Optional as return type to avoid potential performance decrease.
`List<MethodDescriptor>`	`getMethods(String methodName)`
`Class<?>`	`getServiceInterfaceClass()`
`String`	`getServiceName()`

public ServiceDescriptor(Class<?> interfaceClass)

public Class<?> getServiceInterfaceClass()

public Set<MethodDescriptor> getAllMethods()

public MethodDescriptor getMethod(String methodName,
                                  String params)

Does not use Optional as return type to avoid potential performance decrease.

public MethodDescriptor getMethod(String methodName,
                                  Class<?>[] paramTypes)

Does not use Optional as return type to avoid potential performance decrease.

public List<MethodDescriptor> getMethods(String methodName)

Class ServiceDescriptor