Support for Intl.DurationFormat

[Ericlm]

Clear and concise description of the problem

Currently, vue-i18n supports number formatting and datetime formatting with $n and $d. It would be great if it could also support Intl DurationFormat.

Suggested solution

I think a new function would be needed ($n for numbers, $d for datetime, maybe $u (dUration)) or $du ? This function could be just like number or datetime formats, with formats for each language, and a default that would be the one of Intl.

Alternative

For now, I'm using NumberFormat as it is the way duration works anyway, but that would be cool if it was supported in vuei18n.

Additional context

https://moment.github.io/luxon/api-docs/index.html#durationtohuman (which uses NumberFormat), and about this new Intl object that is specialized in formatting durations. :sli

Validations

• Read the Contributing Guidelines
• Read the Documentation
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.