Support ref.focus() alias

[danilofuchs]

Is your feature request related to a problem? Please describe. When using react-hook-form, it's ability to focus on the input automatically on error uses ref.focus().

However, react-datepicker uses the nomenclature ref.setFocus()

Describe the solution you'd like An alias ref.focus() to allow better compatibility with the ecosystem

Describe alternatives you've considered

• Intercepting the ref myself, calling ref.setFocus():

  const innerRef = useRef<ReactDatePicker>(null);
  
  useImperativeHandle(ref, () => ({
    focus: () => innerRef.current?.setFocus(),
  }));
  
  return (
    <ReactDatePicker
      ref={innerRef}
    />
  )

• Deprecating setFocus(), setBlur(), etc.
• Use customInputRef, but it only allows legacy string refs

Additional context https://react-hook-form.com/docs/useform/setfocus