push: use `exchange.push` in `commands.push`

To gain access to all results from the push, we need to have access to the
`pushoperation` object. We call `exchange.push` to do so.

It is impossible to just change the `localrepo.push` signature because the
change may be too subtle to be caught by external extension wrapping
`localrepo.push`.

This mean we'll have to kill `localrepo.push` because just using
`exchange.push` in `commands.py` would silently disable all wrapping around
`localrepo.push` by third-party extensions. So we'll remove it in a later
changeset to get such extensions to fail noisily.

mercurial/commands.py

@@ -5068,10 +5068,10 b' def push(ui, repo, dest=None, **opts):'
                 return not result
     finally:
         del repo._subtoppath
-    result = repo.push(other, opts.get('force'), revs=revs,
-                       newbranch=opts.get('new_branch'))
-
-    result = not result
+    pushop = exchange.push(repo, other, opts.get('force'), revs=revs,
+                           newbranch=opts.get('new_branch'))
+
+    result = not pushop.cgresult
 
     if opts.get('bookmark'):
         bresult = bookmarks.pushtoremote(ui, repo, other, opts['bookmark'])