Prevent duplicate validation issues for subpackage validation

Often a validator is called twice on the same package:

• In the context of a standalone package (triggered from a non-container Maven module)
• In the context as subpackage inside a container module

Currently lots of validators emit duplicate reports and also settings often needs to be copied over to the container package.

Therefore with default settings validators should prevent emitting issues twice but preferably only in the first context. The second context should only emit issues which cannot be detected for the standalone case.