Introduce settings profiles (#35339)

Settings Profiles

- [X] Allow profiles to be defined, where each profile can be any of
Zed's settings
    - [X] Autocompletion of all settings
    - [X] Errors on invalid keys
- [X] Action brings up modal that shows user-defined profiles
- [X] Alphabetize profiles
- [X] Ability to filter down via keyboard, and navigate via arrow up and
down
- [X] Auto select Disabled option by default (first in list, after
alphabetizing user-defined profiles)
- [X] Automatically select active profile on next picker summoning
- [X] Persist settings until toggled off
- [X] Show live preview as you select from the profile picker
- [X] Tweaking a setting, while in a profile, updates the profile live
- [X] Make sure actions that live update Zed, such as `cmd-0`, `cmd-+`,
and `cmd--`, work while in a profile
- [X] Add a test to track state

Release Notes:

- Added the ability to configure settings profiles, via the "profiles"
key. Example:

```json
{
  "profiles": {
    "Streaming": {
      "agent_font_size": 20,
      "buffer_font_size": 20,
      "theme": "One Light",
      "ui_font_size": 20
    }
  }
}
```

To set a profile, use `settings profile selector: toggle`

crates/settings/src/settings.rs

@@ -7,7 +7,7 @@ mod settings_json;
 mod settings_store;
 mod vscode_import;
 
-use gpui::App;
+use gpui::{App, Global};
 use rust_embed::RustEmbed;
 use std::{borrow::Cow, fmt, str};
 use util::asset_str;
@@ -27,6 +27,11 @@ pub use settings_store::{
 };
 pub use vscode_import::{VsCodeSettings, VsCodeSettingsSource};
 
+#[derive(Clone, Debug, PartialEq)]
+pub struct ActiveSettingsProfileName(pub String);
+
+impl Global for ActiveSettingsProfileName {}
+
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash, PartialOrd, Ord)]
 pub struct WorktreeId(usize);
 
@@ -74,6 +79,7 @@ pub fn init(cx: &mut App) {
         .unwrap();
     cx.set_global(settings);
     BaseKeymap::register(cx);
+    SettingsStore::observe_active_settings_profile_name(cx).detach();
 }
 
 pub fn default_settings() -> Cow<'static, str> {