Move `configurationAttributesSchema` down to `DependencyHandler` This commit fixes gradle/performance#251 by moving the attributes schema to the dependency handler. It's worth noting that is also renames the configuration method from `configurationAttributesSchema` to simply `attributesSchema`.
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.