rust: Make OwningDirstateMap generic and move it into hg-core This will enable using it in rhg too. The `OwningDirstateMap::new_empty` constructor is generic and accepts a value of any type that gives acces to a bytes buffer. That buffer must stay valid as long as the value hasn?t been dropped, and must keep its memory address even if the value is moved. The `StableDeref` marker trait encodes those constraints. Previously no trait was needed because the value was always of type `PyBytes` which we know satisfies those constraints. The buffer type is ereased in the struct itself through boxing and dynamic dispatch, in order to simplify other signatures that mention `OwningDirstateMap`. Differential Revision: https://phab.mercurial-scm.org/D11396

--- a/rust/hg-core/src/dirstate_tree.rs	Mon Sep 06 13:39:54 2021 +0200
+++ b/rust/hg-core/src/dirstate_tree.rs	Thu Sep 09 18:07:40 2021 +0200
@@ -1,5 +1,7 @@
 pub mod dirstate_map;
 pub mod dispatch;
 pub mod on_disk;
+pub mod owning;
+mod owning_dispatch;
 pub mod path_with_basename;
 pub mod status;