Suite support

[Vampire]

The test suite finder always returns an empty list. But also with JUnit 5 there is suite support: https://junit.org/junit5/docs/current/user-guide/#junit-platform-suite-engine. If there is no dedicated support necessary, there should at least be a test that verifies it works and also works with test classes from different test engines.

[Vampire]

Ah, with the current code it is indeed unnecessary, as any class is just executed for the discovery and thus the suite annotation with all its sibling annotations can just work.

But I still think there should be a test verifying that. :-)