Intertwine: the object brought over leaves no hairline of the one below (#5337)

The area an Intertwine member is drawn over another in was exactly the
overlap face, so its edge lay on the edge of the member below. Both edges
were anti-aliased, and the member below showed through as a thin line along
them. The area now reaches 2 pt past the face into the parts where only the
raised member paints (where drawing it again changes nothing), so its edge
lies inside that member.

docs/gaps.md

@@ -495,7 +495,8 @@ from G14 and the budget run of G15: **~170–270 h** one agent, ~50–80 h wall
   pointer, and a right-click offers Bring to Front, Bring Forward, Send Backward and Send to Back for it in that area
   (`object.intertwine.arrange` with `order` front, forward, backward or back;
   <https://helpx.adobe.com/illustrator/desktop/manage-objects/reshape-transform-objects/create-intertwined-objects.html>).
-  The group renders, saves and exports through its live expansion. Still missing: adding objects to the group by
+  The group renders, saves and exports through its live expansion; an object brought over another shows no hairline
+  of the one below along that object's edges (#5337). Still missing: adding objects to the group by
   dragging them in the Layers panel is untested.
 - **Done (from users' reports):** Object › Create Gradient Mesh on an embedded image turns it into a mesh over its
   rectangle, with the image's transform kept; each point takes the average colour and opacity of the picture around it