don't show the feature value in an explanatory assertion group

[robstoll]

Platform (all, jvm, js): all
Extension (none, kotlin 1.3): none

Code related feature

if a feature assertion is used in an explanatory assertion group then we should not show the coresponding representation of the feature, because it could be wrong, should not have a relevance as the subject is not available. For instance, we show sometimes that -1 matches where found. Thus:

• adjust TextFeatureAssertionGroupFormatter don't show representation in case we are in an explanatory assertion group (track again separately).