fix(patch): cherry-pick 45faf4d to release/v0.34.0-preview.0-pr-22148 [CONFLICTS] (#22174)

Co-authored-by: Jack Wotherspoon <jackwoth@google.com>
Co-authored-by: Christine Betts <chrstn@uw.edu>

packages/cli/src/ui/themes/theme-manager.ts

@@ -241,6 +241,17 @@ class ThemeManager {
     }
   }
 
+  /**
+   * Checks if themes for a given extension are already registered.
+   * @param extensionName The name of the extension.
+   * @returns True if any themes from the extension are registered.
+   */
+  hasExtensionThemes(extensionName: string): boolean {
+    return Array.from(this.extensionThemes.keys()).some((name) =>
+      name.endsWith(`(${extensionName})`),
+    );
+  }
+
   /**
    * Clears all registered extension themes.
    * This is primarily for testing purposes to reset state between tests.