repoview: keep the branchmap cache for the `served.hidden` view warm

For the same reason we want to keep the cache for the `served` view up to date,
we want to also keep the `served.hidden` view up to date. If some processes with
a readonly access to the repo needs to access it, we better have the cache warm
to avoid computing the same data over and over and over.

In most case (no secret changesets), the "served" and "served.hidden" set will
be identical and no cache will actually have to be updated.

mercurial/localrepo.py

@@ -2107,6 +2107,7 b' class localrepository(object):'
             # accessing the 'ser ved' branchmap should refresh all the others,
             self.ui.debug('updating the branch cache\n')
             self.filtered('served').branchmap()
+            self.filtered('served.hidden').branchmap()
 
         if full:
             unfi = self.unfiltered()

tests/test-rebase-conflicts.t

@@ -330,6 +330,7 b' Check that the right ancestors is used w'
   bundle2-input-bundle: 2 parts total
   updating the branch cache
   invalid branchheads cache (served): tip differs
+  invalid branchheads cache (served.hidden): tip differs
   rebase completed
 
 Test minimization of merge conflicts

tests/test-remote-hidden.t

@@ -72,6 +72,20 b' Testing the `served.hidden` view'
 Test the feature
 ================
 
+Check cache pre-warm
+--------------------
+
+  $ ls -1 repo-with-hidden/.hg/cache
+  branch2
+  branch2-base
+  branch2-served
+  branch2-served.hidden
+  branch2-visible
+  rbc-names-v1
+  rbc-revs-v1
+  tags2
+  tags2-visible
+
 Check that the `served.hidden` repoview
 ---------------------------------------