rust: move rustfmt.toml to repo root so it can be used by `hg fix` `hg fix` runs the formatters from the repo root so it doesn't pick up the `rustfmt.toml` configs we had in each the `hg-core`, `hg-cpython`, and `rhg` packages, which resulted in warnings about `async fn` not existing in Rust 2015. This patch moves the `rustfmt.toml` file to the root so `hg fix` will use it. By putting the `rustfmt.toml` file in a higher-level directory, it also applies to the `chg` and `hgcli` packages. That makes `test-check-rust-format.t` fail, so this patch also applies the new formatting rules to those packages. Differential Revision: https://phab.mercurial-scm.org/D9142

[fix]
clang-format:command = clang-format --style file
clang-format:pattern = set:(**.c or **.cc or **.h) and not "include:contrib/clang-format-ignorelist"

rustfmt:command = rustfmt +nightly
rustfmt:pattern = set:"**.rs" - "mercurial/thirdparty/**"

black:command = black --config=black.toml -
black:pattern = set:**.py - mercurial/thirdparty/**

# Mercurial doesn't have any Go code, but if we did this is how we
# would configure `hg fix` for Go:
go:command = gofmt
go:pattern = set:**.go