STYLE: rebase edge on labelPair, additional methods in Pair

- use FixedList first/last in Pair first/second

- consistent first/second access for line

applications/utilities/surface/surfaceFeatureExtract/surfaceFeatureExtract.C

@@ -368,7 +368,7 @@ int main(int argc, char *argv[])
             faces.setSize(surf.size());
             forAll(surf, fi)
             {
-                faces[fi] = surf[fi].triFaceFace();
+                faces[fi] = surf[fi];
             }
         }