bookmark: use `list_paths` to access path definition

The content of the `[paths]` config section is receiving transformation that
make it hard to recognise whats the actual name, and the next changeset will
make it worse. So we use the official API for this instead.

Differential Revision: https://phab.mercurial-scm.org/D10448

mercurial/bookmarks.py

@@ -600,11 +600,12 b' def _diverge(ui, b, path, localmarks, re'
     # if an @pathalias already exists, we overwrite (update) it
     if path.startswith(b"file:"):
         path = urlutil.url(path).path
-    for p, u in ui.configitems(b"paths"):
-        if u.startswith(b"file:"):
-            u = urlutil.url(u).path
-        if path == u:
-            return b'%s@%s' % (b, p)
+    for name, p in urlutil.list_paths(ui):
+        loc = p.rawloc
+        if loc.startswith(b"file:"):
+            loc = urlutil.url(loc).path
+        if path == loc:
+            return b'%s@%s' % (b, name)
 
     # assign a unique "@number" suffix newly
     for x in range(1, 100):