pub fn to_feature_query(&self, filter: impl FeatureFilter<'g>) -> FeatureQuery<'g> {
        let package_ixs = self.params.initials();
        let feature_graph = self.graph.feature_graph();
        let feature_ixs =
            feature_graph.feature_ixs_for_package_ixs_filtered(package_ixs.iter().copied(), filter);
        feature_graph.query_from_parts(feature_ixs, self.direction())
    }
Converts this `PackageQuery` into a `FeatureQuery`, using the given feature filter.

This will cause the feature graph to be constructed if it hasn't been done so already.
guppy/src/graph/query.rs