class<abstract> doesn't work across multiple files.

deriving from a class in another verse file leads to this error:

`concrete` classes must not inherit from `abstract` classes of other modules.  `concrete` class `test_class` inherits from `abstract` class `test_class_base`.(3632)

I would appreciate that feature, so using multiple verse files won’t render abstract classes entirely useless.

@Daigoro Thank you for your feedback. While I cannot guarantee a response, I can confirm that this has been forwarded to the appropriate team.