Reland "Remove cx from ThemeSettings" (#39720)

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

Closes #ISSUE

Release Notes:

- N/A

crates/project_panel/src/project_panel_settings.rs

@@ -55,7 +55,7 @@ impl ScrollbarVisibility for ProjectPanelSettings {
 }
 
 impl Settings for ProjectPanelSettings {
-    fn from_settings(content: &settings::SettingsContent, _cx: &mut ui::App) -> Self {
+    fn from_settings(content: &settings::SettingsContent) -> Self {
         let project_panel = content.project_panel.clone().unwrap();
         Self {
             button: project_panel.button.unwrap(),