fix: LinkedHashSet for deterministic computeAllFeatureNames

Author: pmbittner

src/main/java/org/variantsync/diffdetective/variation/diff/VariationDiff.java

@@ -35,7 +35,7 @@
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.HashMap;
-import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -383,7 +383,7 @@ public int count(final Predicate<DiffNode<L>> nodesToCount) {
      * @return A set of every occuring feature name.
      */
     public Set<String> computeAllFeatureNames() {
-        Set<String> features = new HashSet<>();
+        Set<String> features = new LinkedHashSet<>();
         forAll(node -> {
                 if (node.isConditionalAnnotation()) {
                     features.addAll(node.getFormula().getUniqueContainedFeatures());