Change batch issue validation to consider issues with "disconnected" main context as invalid
There are cases where an issue source can end up managing issues that have a link to an issue context, but the context resource is can be considered disconnected from the index root/model that contains the issue source.
Here disconnected means that the resource does not have non-asserted statements which do not point to
- the resource itself
- the issue that linked to its context
Also L0.InstanceOf
does not count as an external link.