[ty] Move SystemOrVendoredPathRef

This moves the type and adds a few methods so that it can
be used elsewhere.

crates/ruff_db/src/vendored/path.rs

@@ -17,6 +17,10 @@ impl VendoredPath {
         unsafe { &*(path as *const Utf8Path as *const VendoredPath) }
     }
 
+    pub fn file_name(&self) -> Option<&str> {
+        self.0.file_name()
+    }
+
     pub fn to_path_buf(&self) -> VendoredPathBuf {
         VendoredPathBuf(self.0.to_path_buf())
     }