exchange: expand usage of getchangegroupraw

The 'getchangegroupraw' is very simple (two lines) so we inline it in its only
caller. This exposes the 'outgoing' object of the part generator function, allowing
us to add information on the number of changesets contained in the part in a
later changeset. Such information is useful for progress bar.

mercurial/exchange.py

@@ -1294,10 +1294,10 b' def _getbundlechangegrouppart(bundler, r'
             if not cgversions:
                 raise ValueError(_('no common changegroup version'))
             version = getcgkwargs['version'] = max(cgversions)
-        cg = changegroup.getchangegroupraw(repo, source, heads=heads,
-                                           common=common,
-                                           bundlecaps=bundlecaps,
-                                           **getcgkwargs)
+        outgoing = changegroup.computeoutgoing(repo, heads, common)
+        cg = changegroup.getlocalchangegroupraw(repo, source, outgoing,
+                                                bundlecaps=bundlecaps,
+                                                **getcgkwargs)
 
     if cg:
         part = bundler.newpart('changegroup', data=cg)