Add a subcommand to generate dependency graphs (#13402)

## Summary

This PR adds an experimental Ruff subcommand to generate dependency
graphs based on module resolution.

A few highlights:

- You can generate either dependency or dependent graphs via the
`--direction` command-line argument.
- Like Pants, we also provide an option to identify imports from string
literals (`--detect-string-imports`).
- Users can also provide additional dependency data via the
`include-dependencies` key under `[tool.ruff.import-map]`. This map uses
file paths as keys, and lists of strings as values. Those strings can be
file paths or globs.

The dependency resolution uses the red-knot module resolver which is
intended to be fully spec compliant, so it's also a chance to expose the
module resolver in a real-world setting.

The CLI is, e.g., `ruff graph build ../autobot`, which will output a
JSON map from file to files it depends on for the `autobot` project.

crates/ruff_db/src/system/path.rs

@@ -593,6 +593,27 @@ impl ruff_cache::CacheKey for SystemPathBuf {
     }
 }
 
+#[cfg(feature = "serde")]
+impl serde::Serialize for SystemPath {
+    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        self.0.serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl serde::Serialize for SystemPathBuf {
+    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        self.0.serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> serde::Deserialize<'de> for SystemPathBuf {
+    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        Utf8PathBuf::deserialize(deserializer).map(SystemPathBuf)
+    }
+}
+
 /// A slice of a virtual path on [`System`](super::System) (akin to [`str`]).
 #[repr(transparent)]
 pub struct SystemVirtualPath(str);