settings ui: Create settings key trait (#37489)

This PR separates out the associated constant `KEY` from the `Settings`
trait into a new trait `SettingsKey`. This allows for the key trait to
be derived using attributes to specify the path so that the new
`SettingsUi` derive macro can use the same attributes to determine top
level settings paths thereby removing the need to duplicate the path in
both `Settings::KEY` and `#[settings_ui(path = "...")]`

Co-authored-by: Ben Kunkle <ben@zed.dev>

Release Notes:

- N/A

---------

Co-authored-by: Ben Kunkle <ben@zed.dev>

crates/language/src/language_settings.rs

@@ -17,7 +17,8 @@ use serde::{
 };
 
 use settings::{
-    ParameterizedJsonSchema, Settings, SettingsLocation, SettingsSources, SettingsStore, SettingsUi,
+    ParameterizedJsonSchema, Settings, SettingsKey, SettingsLocation, SettingsSources,
+    SettingsStore, SettingsUi,
 };
 use shellexpand;
 use std::{borrow::Cow, num::NonZeroU32, path::Path, slice, sync::Arc};
@@ -292,7 +293,10 @@ pub struct CopilotSettings {
 }
 
 /// The settings for all languages.
-#[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize, JsonSchema, SettingsUi)]
+#[derive(
+    Debug, Clone, Default, PartialEq, Serialize, Deserialize, JsonSchema, SettingsUi, SettingsKey,
+)]
+#[settings_key(None)]
 pub struct AllLanguageSettingsContent {
     /// The settings for enabling/disabling features.
     #[serde(default)]
@@ -1213,8 +1217,6 @@ impl InlayHintKind {
 }
 
 impl settings::Settings for AllLanguageSettings {
-    const KEY: Option<&'static str> = None;
-
     type FileContent = AllLanguageSettingsContent;
 
     fn load(sources: SettingsSources<Self::FileContent>, _: &mut App) -> Result<Self> {