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/project.rs

@@ -2579,7 +2579,7 @@ impl Project {
         language_name: LanguageName,
     ) -> Option<SharedString> {
         languages
-            .language_for_name(&language_name.0)
+            .language_for_name(language_name.as_ref())
             .await
             .ok()?
             .toolchain_lister()