[TS] add Icon as default export

[superhawk610]

This PR adds Icon as the default export in the TS module declaration.

The original JS export can be seen here

import { Icon, withBaseIcon } from './Icon';
import { horizontalCenter } from './horizontalCenter';

export { withBaseIcon };
export { Icon };
export { horizontalCenter };
export default Icon; // <-- here

[wmira]

@superhawk610 thanks, will have this published