theme: Split out theme_settings crate (#52569)

Self-Review Checklist:

- [ ] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A

crates/picker/Cargo.toml

@@ -22,6 +22,7 @@ menu.workspace = true
 schemars.workspace = true
 serde.workspace = true
 theme.workspace = true
+theme_settings.workspace = true
 ui.workspace = true
 ui_input.workspace = true
 workspace.workspace = true

crates/picker/src/picker.rs

@@ -16,7 +16,7 @@ use serde::Deserialize;
 use std::{
     cell::Cell, cell::RefCell, collections::HashMap, ops::Range, rc::Rc, sync::Arc, time::Duration,
 };
-use theme::ThemeSettings;
+use theme_settings::ThemeSettings;
 use ui::{
     Color, Divider, DocumentationAside, DocumentationSide, Label, ListItem, ListItemSpacing,
     ScrollAxes, Scrollbars, WithScrollbar, prelude::*, utils::WithRemSize, v_flex,
@@ -955,7 +955,7 @@ mod tests {
         cx.update(|cx| {
             let store = settings::SettingsStore::test(cx);
             cx.set_global(store);
-            theme::init(theme::LoadThemes::JustBase, cx);
+            theme_settings::init(theme::LoadThemes::JustBase, cx);
             editor::init(cx);
         });
     }