Add overload of TestWatcher.skipped() that uses the external AssumptionViolationException

Add overload of TestWatcher.skipped() that uses the external AssumptionViolationException

This allows code using TestWatcher to handle assumption violation exceptions
without using deprecated classes.
Could you move this class down after `neitherLogSuccessNorFailedForViolatedAssumption` The internal classes are always positioned above the test that is using them.