engine: make hook point for extension a public function

Well there are no private public functions in Python, but we generally treat
functions and variables starting with `_` as private ones.

A function which needs to be overrided in extension should be a public one.

Differential Revision: https://phab.mercurial-scm.org/D9672

hgext/lfs/wrapper.py

@@ -524,7 +524,7 b' def uploadblobs(repo, pointers):'
     remoteblob.writebatch(pointers, repo.svfs.lfslocalblobstore)
 
 
[e-mail](upgrade_engine, b'_finishdatamigration')
[e-mail](upgrade_engine, b'finishdatamigration')
 def upgradefinishdatamigration(orig, ui, srcrepo, dstrepo, requirements):
     orig(ui, srcrepo, dstrepo, requirements)
 

mercurial/upgrade_utils/engine.py

@@ -408,7 +408,7 b' def _filterstorefile(srcrepo, dstrepo, r'
     return True
 
 
-def _finishdatamigration(ui, srcrepo, dstrepo, requirements):
+def finishdatamigration(ui, srcrepo, dstrepo, requirements):
     """Hook point for extensions to perform additional actions during upgrade.
 
     This function is called after revlogs and store files have been copied but
@@ -458,7 +458,7 b' def upgrade(ui, srcrepo, dstrepo, upgrad'
         dst = dstrepo.store.rawvfs.join(p)
         util.copyfile(src, dst, copystat=True)
 
-    _finishdatamigration(ui, srcrepo, dstrepo, requirements)
+    finishdatamigration(ui, srcrepo, dstrepo, requirements)
 
     ui.status(_(b'data fully migrated to temporary repository\n'))