dirstate: issue a developer warning on implicit write on wlock release

Our goal is to get rid of all these to clarify the writing pattern, so it is
time to warn about this (and later, forbid it).

mercurial/localrepo.py

@@ -3075,6 +3075,9 b' class localrepository:'
                 self.ui.develwarn(msg)
                 self.dirstate.invalidate()
             else:
+                if self.dirstate._dirty:
+                    msg = b"dirty dirstate on wlock release"
+                    self.ui.develwarn(msg)
                 self.dirstate.write(None)
 
             self._filecache[b'dirstate'].refresh()