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/project/src/project_settings.rs

@@ -18,8 +18,8 @@ use rpc::{
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use settings::{
-    InvalidSettingsError, LocalSettingsKind, Settings, SettingsLocation, SettingsSources,
-    SettingsStore, SettingsUi, parse_json_with_comments, watch_config_file,
+    InvalidSettingsError, LocalSettingsKind, Settings, SettingsKey, SettingsLocation,
+    SettingsSources, SettingsStore, SettingsUi, parse_json_with_comments, watch_config_file,
 };
 use std::{
     collections::BTreeMap,
@@ -36,7 +36,8 @@ use crate::{
     worktree_store::{WorktreeStore, WorktreeStoreEvent},
 };
 
-#[derive(Debug, Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
+#[derive(Debug, Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi, SettingsKey)]
+#[settings_key(None)]
 pub struct ProjectSettings {
     /// Configuration for language servers.
     ///
@@ -568,8 +569,6 @@ impl Default for SessionSettings {
 }
 
 impl Settings for ProjectSettings {
-    const KEY: Option<&'static str> = None;
-
     type FileContent = Self;
 
     fn load(sources: SettingsSources<Self::FileContent>, _: &mut App) -> anyhow::Result<Self> {