settings ui: Start work on creating the initial structure (#36904)

## Goal 

This PR creates the initial settings ui structure with the primary goal
of making a settings UI that is
- Comprehensive: All settings are available through the UI
- Correct: Easy to understand the underlying JSON file from the UI
- Intuitive
- Easy to implement per setting so that UI is not a hindrance to future
settings changes

### Structure

The overall structure is settings layer -> data layer -> ui layer.

The settings layer is the pre-existing settings definitions, that
implement the `Settings` trait. The data layer is constructed from
settings primarily through the `SettingsUi` trait, and it's associated
derive macro. The data layer tracks the grouping of the settings, the
json path of the settings, and a data representation of how to render
the controls for the setting in the UI, that is either a marker value
for the component to use (avoiding a dependency on the `ui` crate) or a
custom render function.

Abstracting the data layer from the ui layer allows crates depending on
`settings` to implement their own UI without having to add additional UI
dependencies, thus avoiding circular dependencies. In cases where custom
UI is desired, and a creating a custom render function in the same crate
is infeasible due to circular dependencies, the current solution is to
implement a marker for the component in the `settings` crate, and then
handle the rendering of that component in `settings_ui`.

### Foundation 

This PR creates a macro and a trait both called `SettingsUi`. The
`SettingsUi` trait is added as a new trait bound on the `Settings`
trait, this allows the type system to guarantee that all settings
implement UI functionality. The macro is used to derived the trait for
most types, and can be modified through attributes for unique cases as
well.

A derive-macro is used to generate the settings UI trait impl, allowing
it the UI generation to be generated from the static information in our
code base (`default.json`, Struct/Enum names, field names, `serde`
attributes, etc). This allows the UI to be auto-generated for the most
part, and ensures consistency across the UI.


#### Immediate Follow ups

- Add a new `SettingsPath` trait that will be a trait bound on
`SettingsUi` and `Settings`
- This trait will replace the `Settings::key` value to enable
`SettingsUi` to infer the json path of it's derived type
- Figure out how to render `Option<T> where T: SettingsUi` correctly
- Handle `serde` attributes in the `SettingsUi` proc macro to correctly
get json path from a type's field and identity

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};
+use settings::{Settings, SettingsLocation, SettingsSources, SettingsUi};
 use smallvec::SmallVec;
 use std::{
     any::{Any, TypeId},
@@ -49,7 +49,7 @@ impl Default for SaveOptions {
     }
 }
 
-#[derive(Deserialize)]
+#[derive(Deserialize, SettingsUi)]
 pub struct ItemSettings {
     pub git_status: bool,
     pub close_position: ClosePosition,
@@ -59,7 +59,7 @@ pub struct ItemSettings {
     pub show_close_button: ShowCloseButton,
 }
 
-#[derive(Deserialize)]
+#[derive(Deserialize, SettingsUi)]
 pub struct PreviewTabsSettings {
     pub enabled: bool,
     pub enable_preview_from_file_finder: bool,

crates/workspace/src/workspace_settings.rs

@@ -6,9 +6,9 @@ use collections::HashMap;
 use gpui::App;
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
-use settings::{Settings, SettingsSources};
+use settings::{Settings, SettingsSources, SettingsUi};
 
-#[derive(Deserialize)]
+#[derive(Deserialize, SettingsUi)]
 pub struct WorkspaceSettings {
     pub active_pane_modifiers: ActivePanelModifiers,
     pub bottom_dock_layout: BottomDockLayout,
@@ -216,7 +216,7 @@ pub struct WorkspaceSettingsContent {
     pub zoomed_padding: Option<bool>,
 }
 
-#[derive(Deserialize)]
+#[derive(Deserialize, SettingsUi)]
 pub struct TabBarSettings {
     pub show: bool,
     pub show_nav_history_buttons: bool,