Reland "Remove cx from ThemeSettings" (#39720)

- **Reapply "Remove cx from ThemeSettings (#38836)" (#39691)**
- **Fix theme loading races**

Closes #ISSUE

Release Notes:

- N/A

crates/title_bar/src/title_bar_settings.rs

@@ -1,5 +1,4 @@
 use settings::{Settings, SettingsContent};
-use ui::App;
 
 #[derive(Copy, Clone, Debug)]
 pub struct TitleBarSettings {
@@ -13,7 +12,7 @@ pub struct TitleBarSettings {
 }
 
 impl Settings for TitleBarSettings {
-    fn from_settings(s: &SettingsContent, _: &mut App) -> Self {
+    fn from_settings(s: &SettingsContent) -> Self {
         let content = s.title_bar.clone().unwrap();
         TitleBarSettings {
             show_branch_icon: content.show_branch_icon.unwrap(),