perf: use storage API for resolving manifest node lookup() isn't part of the storage API. And this code shouldn't be accessing manifestlog._revlog directly for the modern code base. So let's port it to the modern API. Note that the previous code was busted for cases where we needed to call lookup() because lookup() isn't exposed by manifestrevlog any more. This change is strictly BC breaking because we no longer support resolving partial nodes. But it is a perf* command and I don't think we should flag the change as such. Differential Revision: https://phab.mercurial-scm.org/D4390