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/language/src/language.rs

@@ -852,11 +852,7 @@ struct BracketConfig {
 
 impl Language {
     pub fn new(config: LanguageConfig, ts_language: Option<tree_sitter::Language>) -> Self {
-        Self::new_with_id(
-            LanguageId(NEXT_LANGUAGE_ID.fetch_add(1, SeqCst)),
-            config,
-            ts_language,
-        )
+        Self::new_with_id(LanguageId::new(), config, ts_language)
     }
 
     fn new_with_id(
@@ -1569,44 +1565,9 @@ mod tests {
     use super::*;
     use gpui::TestAppContext;
 
-    #[gpui::test(iterations = 10)]
-    async fn test_first_line_pattern(cx: &mut TestAppContext) {
-        let mut languages = LanguageRegistry::test();
-
-        languages.set_executor(cx.executor());
-        let languages = Arc::new(languages);
-        languages.register_test_language(LanguageConfig {
-            name: "JavaScript".into(),
-            matcher: LanguageMatcher {
-                path_suffixes: vec!["js".into()],
-                first_line_pattern: Some(Regex::new(r"\bnode\b").unwrap()),
-            },
-            ..Default::default()
-        });
-
-        languages
-            .language_for_file("the/script".as_ref(), None)
-            .await
-            .unwrap_err();
-        languages
-            .language_for_file("the/script".as_ref(), Some(&"nothing".into()))
-            .await
-            .unwrap_err();
-        assert_eq!(
-            languages
-                .language_for_file("the/script".as_ref(), Some(&"#!/bin/env node".into()))
-                .await
-                .unwrap()
-                .name()
-                .as_ref(),
-            "JavaScript"
-        );
-    }
-
     #[gpui::test(iterations = 10)]
     async fn test_language_loading(cx: &mut TestAppContext) {
-        let mut languages = LanguageRegistry::test();
-        languages.set_executor(cx.executor());
+        let languages = LanguageRegistry::test(cx.executor());
         let languages = Arc::new(languages);
         languages.register_native_grammars([
             ("json", tree_sitter_json::language()),