copies: extract method for getting non-wdir forward copies I may add an alternative way of getting copy metadata (from changelog, not filelog) but the chaining with the dirstate copy metadata will be the same, so it will probably help to have this extracted. Even if that doesn't happen, the next patch will show that we can simplify this a bit after this refactoring, so it seems worth it regardless. Differential Revision: https://phab.mercurial-scm.org/D1697