MBS-11806: Don't group relationships for different track sets (metabrainz#2186)

As far as I can tell, this code was written for relationships
that apply to one entity only (one recording, one release...).
As such, there was never a need to check for more than
"are the rels related, and are the attributes the same".
But this now also used for grouped display of medium relationships
under a release, and that involves relationships from different tracks.
Nothing in the code checked whether the tracks actually
matched before they got combined - one of the sets of tracks
would just get dropped when combining the two relationship
groups. This now makes sure that the tracks also match, if they exist,
before allowing a merged display of the relationship.

Author: reosarevok

root/utility/groupRelationships.js

@@ -114,14 +114,25 @@ const areDatedExtraAttributesEqual = (a, b) => (
   arraysEqual(a.attributes, b.attributes, areLinkAttrsEqual)
 );
 
-const areRelationshipTargetGroupsEqual = (a, b) => (
-  a.key === b.key &&
-  arraysEqual(
-    a.datedExtraAttributesList,
-    b.datedExtraAttributesList,
-    areDatedExtraAttributesEqual,
-  )
-);
+const areRelationshipTargetGroupsEqual = (a, b) => {
+  const aTracks = a.tracks;
+  const bTracks = b.tracks;
+
+  return (
+    a.key === b.key &&
+    arraysEqual(
+      a.datedExtraAttributesList,
+      b.datedExtraAttributesList,
+      areDatedExtraAttributesEqual,
+    ) &&
+    (aTracks && bTracks)
+      ? arraysEqual(
+        Array.from(aTracks),
+        Array.from(bTracks),
+        (a, b) => a === b,
+      ) : true
+  );
+};
 
 function displayLinkPhrase(linkTypeInfo) {
   const phrase = linkTypeInfo.phrase;