feat: export CSSStyleSheet as default from CSSResult-in-js files

PiperOrigin-RevId: 876734116

Author: asyncliz

scripts/css-to-ts.ts

@@ -28,5 +28,6 @@ fs.writeFileSync(
 // Generated stylesheet for ${cssFilePath}.
 import {css} from 'lit';
 export const styles = css\`${cssContent}\`;
+export default styles.styleSheet!;
 `,
 );