109.23.00

- Exposed `Core.Std.Flags` module.
- Made the `Heap` module implement `Container.S1`.
- Added module `Ref.Permissioned`, which is a ref with `read_only` /
  `read_write` access control.
- Exposed the unique id in `Type_equal.Id`.

  This allows, e.g. hash tables indexed by unique ids.
- Removed the use of `Obj.magic` from the implementation of
  `Type_equal.Id.same`.

  It is not needed because the `Id.t` contains a `Uid.t` and we can
  just use `Uid.equal`.