Add zed://extension/{id} links (#34492)

Release Notes:

- Add zed://extension/{id} links to open the extensions UI with a
specific extension

crates/theme_selector/src/icon_theme_selector.rs

@@ -327,6 +327,7 @@ impl PickerDelegate for IconThemeSelectorDelegate {
                             window.dispatch_action(
                                 Box::new(Extensions {
                                     category_filter: Some(ExtensionCategoryFilter::IconThemes),
+                                    id: None,
                                 }),
                                 cx,
                             );

crates/theme_selector/src/theme_selector.rs

@@ -385,6 +385,7 @@ impl PickerDelegate for ThemeSelectorDelegate {
                             window.dispatch_action(
                                 Box::new(Extensions {
                                     category_filter: Some(ExtensionCategoryFilter::Themes),
+                                    id: None,
                                 }),
                                 cx,
                             );