loading static method
Create a button with loading state
Implementation
static FlintButton loading({
  String text = 'Loading...',
  String? icon,
}) {
  return FlintButton(
    text: text,
    url: '#',
    style: ButtonStyle.secondary(),
    padding: EdgeInsets.symmetric(horizontal: 24.0, vertical: 12.0),
    state: ButtonState.disabled,
    icon: icon ?? '⏳',
  );
}