Add a CurrencyFormatter

[Mordil]

Goal

To remove reliance on Foundation, which leaves us vulnerable to bugs introduced between Swift versions and more control over a nicer API for currency formatting instead of Foundation.NumberFormatter.

Implications

This means that this library will be responsible for vending the necessary parts of ICU to support Localization of currency formats, as well as currency symbols.

This is not a trivial feature

[Mordil]

After several years of thinking about this - I think it's fine to rely on Foundation to avoid duplicating a lot of work for supporting currency formatting.

A lot of the differences between Swift versions is really the difference between ICU versions, which makes sense as it updates to stay current with changing Locales.

I think if this was to be kept as a feature request, what it would end up being is a wrapper around NumberFormatter to highly specialize it for currency and not a general purpose number formatter.

[tonyarnold]

Honestly, most projects should be using Currency Style - my understanding is that the format styles are orders of magnitude faster than the old style Foundation formatters.

[Mordil]

Honestly, most projects should be using Currency Style - my understanding is that the format styles are orders of magnitude faster than the old style Foundation formatters.

That's a good point. I honestly forgot about those APIs 😅