dirstate-tree: Extract into a method sorting children of a given node A later changset will use this in another place. This is an associated function (that Python would call static method) instead of a free function so it doesn’t need to be imported separately. It’s on `Node` rather than `ChildNodes` because the latter is a type alias to an external type (`HashMap`) so that would require an extension trait which needs to be imported separately. Differential Revision: https://phab.mercurial-scm.org/D10721