Add new static Answers RETURNS_DEFAULT_VALUE

[rymsha]

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Mockito v3.6.0

Add new static Answer to Answers: Answers.RETURNS_DEFAULT_VALUE that calls method's getDefaultValue
This would be useful for annotation mocking, especially with MockitoExtension @Mock(answer = Answers.RETURNS_DEFAULT_VALUE)

Background:
In OSGi Annotations are used as "Component Property Type":

public @interface MyConfig { String timeout() default "1s";}

...

@Activate
public void activate(MyConfig config) {timeout = config.timeout();}

verifying the method activate and configuration property default values is problematic.

Current workaround:
mock(MyConfig.class, invocation -> invocation.getMethod().getDefaultValue());

[TimvdLippe]

I think this is a duplicate of #1900

[rymsha]

Yeah, trying to solve the same problem with a different approach, basically.