Improve Javadoc for `@ClassTemplate`, `ParameterDeclarations`, etc.

[sbrannen]

I noticed that the Javadoc for @ClassTemplate, ParameterDeclarations, and related classes can be improved.

For example, @ClassTemplate should consistently refer to "class template", not "container template", "template method", etc; AfterClassTemplateInvocationCallback has some documentation that was copied from BeforeClassTemplateInvocationCallback; ParameterDeclarations cross references java.lang.reflect.Parameter instead of org.junit.jupiter.params.Parameter; and so forth.