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/zed/src/zed/quick_action_bar/repl_menu.rs

@@ -69,7 +69,7 @@ impl QuickActionBar {
                 return self.render_repl_launch_menu(spec, cx);
             }
             SessionSupport::RequiresSetup(language) => {
-                return self.render_repl_setup(&language.0, cx);
+                return self.render_repl_setup(language.as_ref(), cx);
             }
             SessionSupport::Unsupported => return None,
         };