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/editor/src/editor.rs

@@ -7042,7 +7042,7 @@ impl Editor {
             let mut should_rewrap = is_vim_mode == IsVimMode::Yes;
 
             if let Some(language_scope) = buffer.language_scope_at(selection.head()) {
-                match language_scope.language_name().0.as_ref() {
+                match language_scope.language_name().as_ref() {
                     "Markdown" | "Plain Text" => {
                         should_rewrap = true;
                     }