Refactor to use SharedString in more places (#23813)

Splitting this off from
https://github.com/zed-industries/zed/pull/23808, per @maxdeviant's
suggestion!

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/project/src/toolchain_store.rs

@@ -316,7 +316,10 @@ impl LocalToolchainStore {
 
             cx.background_executor()
                 .spawn(async move {
-                    let language = registry.language_for_name(&language_name.0).await.ok()?;
+                    let language = registry
+                        .language_for_name(language_name.as_ref())
+                        .await
+                        .ok()?;
                     let toolchains = language.toolchain_lister()?;
                     Some(toolchains.list(root.to_path_buf(), project_env).await)
                 })