dirstate-tree: Add `WithBasename` wrapper for `HgPath` In the tree-shaped dirstate we want to have nodes representing files or directories, where directory nodes contain a map associating "base" names to child nodes for child files and directories. Many dirstate operations expect a full path from the repository root, but re-concatenating string from nested map keys all the time might be expensive. Instead, `WithBasename` stores a full path for these operations but behaves as its base name (last path component) for equality and comparison. Additionally `inclusive_ancestors` provides the successive map keys that are needed when inserting a new dirstate node at a given full path. Differential Revision: https://phab.mercurial-scm.org/D10365

dirstate-tree: Empty shell for a second Rust DirstateMap implementation For background see description of the previous changeset "Make Rust DirstateMap bindings go through a trait object". Add an empty shell for a opt-in second Rust implementation of the `DirstateMap` type and the `status` function. For now all methods panic. This can be seen in "action" with: ./hg status --config experimental.dirstate-tree.in-memory=1 Differential Revision: https://phab.mercurial-scm.org/D10364

dirstate-tree: Abstract "non-normal" and "other parent" sets Instead of exposing `HashSet`s directly, have slightly higher-level methods for the operations that Python bindings need on them. Differential Revision: https://phab.mercurial-scm.org/D10363