Type definition of lazy loading with dynamic import to `messages` options

[kazupon]

createI18n

const i18n = createI18n({
  messages: {
    en: import('/path/to/en.json').default
  }
}

useI18n

const i18n = useI18n({
  messages: {
    en: import('/path/to/en.json').default
  }
}