project: Fine-grained language server management (#23805)

Closes #ISSUE
https://github.com/zed-industries/zed/pull/23804
Release Notes:

- Improved detection of project roots for use by language servers.

crates/languages/src/rust.rs

@@ -74,6 +74,23 @@ impl LspAdapter for RustLspAdapter {
         Self::SERVER_NAME.clone()
     }
 
+    fn find_project_root(
+        &self,
+        path: &Path,
+        ancestor_depth: usize,
+        delegate: &Arc<dyn LspAdapterDelegate>,
+    ) -> Option<Arc<Path>> {
+        let mut outermost_cargo_toml = None;
+        for path in path.ancestors().take(ancestor_depth) {
+            let p = path.join("Cargo.toml");
+            if delegate.exists(&p, Some(false)) {
+                outermost_cargo_toml = Some(Arc::from(path));
+            }
+        }
+
+        outermost_cargo_toml
+    }
+
     async fn check_if_user_installed(
         &self,
         delegate: &dyn LspAdapterDelegate,