dirstate-v2: Separate iterators for dirfoldmap and debugdirstate `dirstatemap.dirfoldmap` was recently changed to re-use a Rust iterator that was added for the `hg debugdirstate` command. That iterator was based on all nodes in the tree dirstate without an entry only existing to hold child nodes, and therefore being directories. However to optimize status further we may want to store additional nodes for unknown or ignored files and directories. At that point the two users of this iterator will want different things, so let’s make two iterators instead. See doc-comments in `dispatch.rs`. Differential Revision: https://phab.mercurial-scm.org/D11099