Add a setting for custom associations between languages and files (#9290)

Closes #5178

Release Notes:

- Added a `file_types` setting that can be used to associate languages
with file names and file extensions. For example, to interpret all `.c`
files as C++, and files called `MyLockFile` as TOML, add the following
to `settings.json`:

    ```json
    {
      "file_types": {
        "C++": ["c"],
        "TOML": ["MyLockFile"]
      }
    }
    ```

As with most zed settings, this can be configured on a per-directory
basis by including a local `.zed/settings.json` file in that directory.

---------

Co-authored-by: Marshall <marshall@zed.dev>

crates/zed/src/main.rs

@@ -142,9 +142,9 @@ fn main() {
         ));
 
         let client = client::Client::new(clock, http.clone(), cx);
-        let mut languages = LanguageRegistry::new(login_shell_env_loaded);
+        let mut languages =
+            LanguageRegistry::new(login_shell_env_loaded, cx.background_executor().clone());
         let copilot_language_server_id = languages.next_language_server_id();
-        languages.set_executor(cx.background_executor().clone());
         languages.set_language_server_download_dir(paths::LANGUAGES_DIR.clone());
         let languages = Arc::new(languages);
         let node_runtime = RealNodeRuntime::new(http.clone());

crates/zed/src/zed.rs

@@ -3024,15 +3024,18 @@ mod tests {
     async fn test_bundled_languages(cx: &mut TestAppContext) {
         let settings = cx.update(|cx| SettingsStore::test(cx));
         cx.set_global(settings);
-        let mut languages = LanguageRegistry::test();
-        languages.set_executor(cx.executor().clone());
+        let languages = LanguageRegistry::test(cx.executor());
         let languages = Arc::new(languages);
         let node_runtime = node_runtime::FakeNodeRuntime::new();
         cx.update(|cx| {
             languages::init(languages.clone(), node_runtime, cx);
         });
         for name in languages.language_names() {
-            languages.language_for_name(&name).await.unwrap();
+            languages
+                .language_for_name(&name)
+                .await
+                .with_context(|| format!("language name {name}"))
+                .unwrap();
         }
         cx.run_until_parked();
     }