localrepo: create context used for actual commit earlier localrepo.commit creates a workingctx, calls self.status, does some munging on the changes status returns, does some validation on those changes, and then creates a new workingctx from the changes. This moves the creation of the new workginctx ahead of some validation, with the intention of refactoring some of that validation logic into the workingctx, so that it can be reused elsewhere.