treemanifests: store whether a lazydirs entry needs copied after materializing Due to the way that things like manifestlog.get caches its values, without making a copy (if necessary) after calling readsubtree(), we might end up adjusting the state of the same object on different contexts, breaking things like dirty state tracking (and probably other things). Differential Revision: https://phab.mercurial-scm.org/D4874