InferredStatementContext.isConfiguration() forces substatement materialization

We currently use generic method of discovery for isConfiguration(), which means searching all effective statements. This forces materialization of those substatements, which we do not need.

If substatements have been materialized, we should fall back to searching them, but if they were not, we should check parent and and prototype – and make sense of that directly.

This may require a bit of work as we are dealing with completely different assumptions than current utilities handle.