feat(xtask): 'changes' xtask

This will report what commits affect each publishable package and serves
as an alternative to rust-lang#12085.

CI can run this as `cargo changes HEAD~ HEAD^2` and that will capture
all of the commits within the PR (this is the range I used in
`committed`).

There is still work needed to integrate this with an action; this is
just a rough base-line implementation.

I originally tried to use `cargo package --list` to determine what files
belong to what packages but that was taking too long for some reason (it
works well in `cargo release` for my crates).  We can either look into
that in the future or do our own heuristics to filter out content.

.cargo/config.toml

@@ -2,3 +2,4 @@
 build-man = "run --package xtask-build-man --"
 stale-label = "run --package xtask-stale-label --"
 unpublished = "run --package xtask-unpublished --"
+changes = "run --package xtask-changes --"

Cargo.toml

@@ -31,6 +31,7 @@ env_logger = "0.10.0"
 filetime = "0.2.9"
 flate2 = { version = "1.0.3", default-features = false, features = ["zlib"] }
 fwdansi = "1.1.0"
+git-conventional = "0.12.3"
 git2 = "0.17.0"
 git2-curl = "0.18.0"
 gix = { version = "0.44.1", default-features = false, features = ["blocking-http-transport-curl", "progress-tree"] }

crates/xtask-changes/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "xtask-changes"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+anyhow.workspace = true
+cargo.workspace = true
+clap.workspace = true
+env_logger.workspace = true
+git-conventional.workspace = true
+git2.workspace = true
+log.workspace = true
+semver.workspace = true
+termcolor.workspace = true

crates/xtask-changes/src/main.rs

@@ -0,0 +1,15 @@
+mod xtask;
+
+fn main() {
+    env_logger::init_from_env("CARGO_LOG");
+    let cli = xtask::cli();
+    let matches = cli.get_matches();
+
+    let mut config = cargo::util::config::Config::default().unwrap_or_else(|e| {
+        let mut eval = cargo::core::shell::Shell::new();
+        cargo::exit_with_error(e.into(), &mut eval)
+    });
+    if let Err(e) = xtask::exec(&matches, &mut config) {
+        cargo::exit_with_error(e, &mut config.shell())
+    }
+}