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/collab_ui/src/chat_panel.rs

@@ -1042,8 +1042,8 @@ mod tests {
     use util::test::marked_text_ranges;
 
     #[gpui::test]
-    fn test_render_markdown_with_mentions() {
-        let language_registry = Arc::new(LanguageRegistry::test());
+    fn test_render_markdown_with_mentions(cx: &mut AppContext) {
+        let language_registry = Arc::new(LanguageRegistry::test(cx.background_executor().clone()));
         let (body, ranges) = marked_text_ranges("*hi*, «@abc», let's **call** «@fgh»", false);
         let message = channel::ChannelMessage {
             id: ChannelMessageId::Saved(0),
@@ -1090,8 +1090,8 @@ mod tests {
     }
 
     #[gpui::test]
-    fn test_render_markdown_with_auto_detect_links() {
-        let language_registry = Arc::new(LanguageRegistry::test());
+    fn test_render_markdown_with_auto_detect_links(cx: &mut AppContext) {
+        let language_registry = Arc::new(LanguageRegistry::test(cx.background_executor().clone()));
         let message = channel::ChannelMessage {
             id: ChannelMessageId::Saved(0),
             body: "Here is a link https://zed.dev to zeds website".to_string(),
@@ -1130,8 +1130,8 @@ mod tests {
     }
 
     #[gpui::test]
-    fn test_render_markdown_with_auto_detect_links_and_additional_formatting() {
-        let language_registry = Arc::new(LanguageRegistry::test());
+    fn test_render_markdown_with_auto_detect_links_and_additional_formatting(cx: &mut AppContext) {
+        let language_registry = Arc::new(LanguageRegistry::test(cx.background_executor().clone()));
         let message = channel::ChannelMessage {
             id: ChannelMessageId::Saved(0),
             body: "**Here is a link https://zed.dev to zeds website**".to_string(),

crates/collab_ui/src/chat_panel/message_editor.rs

@@ -624,7 +624,7 @@ mod tests {
             MessageEditorSettings::register(cx);
         });
 
-        let language_registry = Arc::new(LanguageRegistry::test());
+        let language_registry = Arc::new(LanguageRegistry::test(cx.executor()));
         language_registry.add(Arc::new(Language::new(
             LanguageConfig {
                 name: "Markdown".into(),