chore(common-tests): add themed test helper (#9763)

Author: jcfranco

packages/calcite-components/src/tests/commonTests/index.ts

@@ -10,5 +10,6 @@ export { focusable } from "./focusable";
 export { formAssociated } from "./formAssociated";
 export { slots } from "./slots";
 export { labelable } from "./labelable";
+export { themed } from "./themed";
 export { t9n } from "./t9n";
 export { HYDRATED_ATTR } from "./utils";