rust-dirstatemap: implement part of the `setparents` logic
The Python code does many round-trip calls to the Rust dirstatemap when copy
information needs to be dropped in `setparents`.
This may result in improved performance on `commit`, `update` and other such
commands, but was mostly done to drop the last use of `set_dirstate_item`.
See inline comments for an asterisk about performance, and see next patch for
why `set_dirstate_item` has to go.
Differential Revision: https://phab.mercurial-scm.org/D12518
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.
Notes for packagers
===================
Mercurial ships a copy of the python-zstandard sources. This is used to
provide support for zstd compression and decompression functionality. The
module is not intended to be replaced by the plain python-zstandard nor
is it intended to use a system zstd library. Patches can result in hard
to diagnose errors and are explicitly discouraged as unsupported
configuration.