Changed artifact selection to select zero or one variant of each node in the dependency graph to be included in the result, whether directly or as an input to a transformation. Artifacts from the selected variant are still filtered by artifact type, which leads to some confusing behaviour. The filtering will be replaced by an error in a later change.
Always perform an equality check at the end of the chain This commit removes the `eventuallyIncompatible`, `eventuallyCompatible` and `addEqualityCheck` methods, and instead systematically add an equality check at the end of the chain. If still after equality check nothing expressed an opinion (this is possible if any value is not present), then we eventually fail.