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/workspace/src/item.rs

@@ -17,7 +17,7 @@ use gpui::{
 use project::{Project, ProjectEntryId, ProjectPath};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
-use settings::{Settings, SettingsLocation, SettingsSources, SettingsUi};
+use settings::{Settings, SettingsKey, SettingsLocation, SettingsSources, SettingsUi};
 use smallvec::SmallVec;
 use std::{
     any::{Any, TypeId},
@@ -101,7 +101,8 @@ pub enum ActivateOnClose {
     LeftNeighbour,
 }
 
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi, SettingsKey)]
+#[settings_key(key = "tabs")]
 pub struct ItemSettingsContent {
     /// Whether to show the Git file status on a tab item.
     ///
@@ -130,7 +131,8 @@ pub struct ItemSettingsContent {
     show_close_button: Option<ShowCloseButton>,
 }
 
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi)]
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, SettingsUi, SettingsKey)]
+#[settings_key(key = "preview_tabs")]
 pub struct PreviewTabsSettingsContent {
     /// Whether to show opened editors as preview tabs.
     /// Preview tabs do not stay open, are reused until explicitly set to be kept open opened (via double-click or editing) and show file names in italic.
@@ -148,8 +150,6 @@ pub struct PreviewTabsSettingsContent {
 }
 
 impl Settings for ItemSettings {
-    const KEY: Option<&'static str> = Some("tabs");
-
     type FileContent = ItemSettingsContent;
 
     fn load(sources: SettingsSources<Self::FileContent>, _: &mut App) -> Result<Self> {
@@ -187,8 +187,6 @@ impl Settings for ItemSettings {
 }
 
 impl Settings for PreviewTabsSettings {
-    const KEY: Option<&'static str> = Some("preview_tabs");
-
     type FileContent = PreviewTabsSettingsContent;
 
     fn load(sources: SettingsSources<Self::FileContent>, _: &mut App) -> Result<Self> {