Reland "Remove cx from ThemeSettings" (#39720)

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

Closes #ISSUE

Release Notes:

- N/A

crates/extension_host/src/extension_settings.rs

@@ -2,7 +2,6 @@ use collections::HashMap;
 use extension::{
     DownloadFileCapability, ExtensionCapability, NpmInstallPackageCapability, ProcessExecCapability,
 };
-use gpui::App;
 use settings::Settings;
 use std::sync::Arc;
 
@@ -37,7 +36,7 @@ impl ExtensionSettings {
 }
 
 impl Settings for ExtensionSettings {
-    fn from_settings(content: &settings::SettingsContent, _cx: &mut App) -> Self {
+    fn from_settings(content: &settings::SettingsContent) -> Self {
         Self {
             auto_install_extensions: content.extension.auto_install_extensions.clone(),
             auto_update_extensions: content.extension.auto_update_extensions.clone(),