extensions_ui: Show the filtered icon theme selector when installing an icon theme (#23992)

This PR makes it so when you install an extension with icon themes it
will deploy the icon theme selector filtered down to the newly-installed
icon themes.

This is similar to what we do when installing an extension with themes.

Because we can only have one picker open at a time, when installing an
extension that has _both_ themes and icon themes, the theme selector
will take precedence.

Release Notes:

- N/A

crates/extensions_ui/src/extensions_ui.rs

@@ -295,6 +295,25 @@ impl ExtensionsPage {
                     );
                 })
                 .ok();
+            return;
+        }
+
+        let icon_themes = extension_store
+            .extension_icon_themes(extension_id)
+            .map(|name| name.to_string())
+            .collect::<Vec<_>>();
+        if !icon_themes.is_empty() {
+            workspace
+                .update(cx, |_workspace, cx| {
+                    window.dispatch_action(
+                        zed_actions::icon_theme_selector::Toggle {
+                            themes_filter: Some(icon_themes),
+                        }
+                        .boxed_clone(),
+                        cx,
+                    );
+                })
+                .ok();
         }
     }