settings_ui: Handle enums with fields (#37945)

Closes #ISSUE

Adds handling for Enums with fields (i.e. not `enum Foo { Yes, No }`) in
Settings UI. Accomplished by creating default values for each element
with fields (in the derive macro), and rendering a toggle button group
with a button for each variant where switching the active variant sets
the value in the settings JSON to the default for the new active
variant.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

---------

Co-authored-by: Conrad <conrad@zed.dev>

crates/language/src/language_settings.rs

@@ -981,11 +981,17 @@ impl<'de> Deserialize<'de> for SelectedFormatter {
 }
 
 /// Controls which formatters should be used when formatting code.
-#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema, SettingsUi)]
 #[serde(untagged)]
 pub enum FormatterList {
     Single(Formatter),
-    Vec(Vec<Formatter>),
+    Vec(#[settings_ui(skip)] Vec<Formatter>),
+}
+
+impl Default for FormatterList {
+    fn default() -> Self {
+        Self::Single(Formatter::default())
+    }
 }
 
 impl AsRef<[Formatter]> for FormatterList {
@@ -998,22 +1004,28 @@ impl AsRef<[Formatter]> for FormatterList {
 }
 
 /// Controls which formatter should be used when formatting code. If there are multiple formatters, they are executed in the order of declaration.
-#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
+#[derive(Clone, Default, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema, SettingsUi)]
 #[serde(rename_all = "snake_case")]
 pub enum Formatter {
     /// Format code using the current language server.
-    LanguageServer { name: Option<String> },
+    LanguageServer {
+        #[settings_ui(skip)]
+        name: Option<String>,
+    },
     /// Format code using Zed's Prettier integration.
+    #[default]
     Prettier,
     /// Format code using an external command.
     External {
         /// The external program to run.
+        #[settings_ui(skip)]
         command: Arc<str>,
         /// The arguments to pass to the program.
+        #[settings_ui(skip)]
         arguments: Option<Arc<[String]>>,
     },
     /// Files should be formatted using code actions executed by language servers.
-    CodeActions(HashMap<String, bool>),
+    CodeActions(#[settings_ui(skip)] HashMap<String, bool>),
 }
 
 /// The settings for indent guides.