revlog: access the nodemap through the index The `revlog.rev` method now access the nodemap through `self.index.nodemap`, instead of using the `_nodecache` attribute that we are trying to remove. This work is part of a refactoring to unify the revlog index and the nodemap. This unification prepare the use of a persistent nodemap. Differential Revision: https://phab.mercurial-scm.org/D7317