Add number formatting missing type definition

[yannbriancon]

Fix typing to match usage in examples https://github.com/intlify/vue-i18n-next/blob/master/docs/guide/essentials/number.md

<p>{{ $n(10000, 'currency') }}</p>
<p>{{ $n(10000, 'currency', 'ja-JP') }}</p>
<p>{{ $n(10000, 'currency', 'ja-JP', { useGrouping: false }) }}</p>
<p>{{ $n(987654321, 'currency', { notation: 'compact' }) }}</p>
<p>{{ $n(0.99123, 'percent') }}</p>
<p>{{ $n(0.99123, 'percent', { minimumFractionDigits: 2 }) }}</p>
<p>{{ $n(12.11612345, 'decimal') }}</p>
<p>{{ $n(12145281111, 'decimal', 'ja-JP') }}</p>

Linked issue: #540

[kazupon]

@yannbriancon
Thank you for your contribution ✨

Oh, I'd forgotten about that. 😅
Thank you!