375a4152fa
Two changes split out from the instability work: * Break `ResolutionGraph::from_state` into methods before adding new logic to it. * `ResolutionGraph`: Convert `NodeKey` type to `PackageRef` struct: Another small refactoring to make subsequent changes easier. No functional changes. @BurntSushi I hope this doesn't interfere with your work too much, the `PackageRef` should at least make debugging panics here easier.