toolchains: Add support for relative paths (#27777)

Closes #ISSUE

Release Notes:

- N/A

crates/language/src/toolchain.rs

@@ -4,7 +4,10 @@
 //! which is a set of tools used to interact with the projects written in said language.
 //! For example, a Python project can have an associated virtual environment; a Rust project can have a toolchain override.
 
-use std::{path::PathBuf, sync::Arc};
+use std::{
+    path::{Path, PathBuf},
+    sync::Arc,
+};
 
 use async_trait::async_trait;
 use collections::HashMap;
@@ -52,6 +55,7 @@ pub trait LanguageToolchainStore {
     async fn active_toolchain(
         self: Arc<Self>,
         worktree_id: WorktreeId,
+        relative_path: Arc<Path>,
         language_name: LanguageName,
         cx: &mut AsyncApp,
     ) -> Option<Toolchain>;